Added 1.21.6 support

Fix FabledSkyBlock errors on new versions of the plugin

.github/workflows/java-ci.yml

@@ -21,7 +21,7 @@ jobs:
           java-version: 21
 
       - name: Setup build cache
-        uses: actions/cache@v2.1.6
+        uses: actions/cache@v4
         with:
           path: ~/.gradle/caches
           key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle.kts') }}
@@ -30,7 +30,7 @@ jobs:
 
       - run: ./gradlew build --full-stacktrace
 
-      - uses: actions/upload-artifact@v2
+#      - uses: actions/upload-artifact@v2
-        with:
+#        with:
-          name: eco-dev-${{ steps.vars.outputs.sha_short }}
+#          name: eco-dev-${{ steps.vars.outputs.sha_short }}
-          path: build/libs
+#          path: build/libs

.github/workflows/publish-release.yml

@@ -19,7 +19,7 @@ jobs:
           java-version: 21
 
       - name: Setup build cache
-        uses: actions/cache@v2.1.6
+        uses: actions/cache@v4
         with:
           path: ~/.gradle/caches
           key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle.kts') }}

.gitignore

@@ -21,4 +21,7 @@ bin/
 gradle-app.setting
 
 # Mac OSX
-.DS_Store
+.DS_Store
+
+# Kotlin
+.kotlin

build.gradle.kts

@@ -1,19 +1,21 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 buildscript {
     repositories {
         mavenCentral()
     }
 
     dependencies {
-        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.9.21")
+        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:2.1.0")
     }
 }
 
 plugins {
     id("java-library")
-    id("io.github.goooler.shadow") version "8.1.7"
+    id("com.gradleup.shadow") version "8.3.5"
     id("maven-publish")
     id("java")
-    kotlin("jvm") version "1.9.21"
+    kotlin("jvm") version "2.1.0"
 }
 
 dependencies {
@@ -32,22 +34,31 @@ dependencies {
     implementation(project(path = ":eco-core:core-nms:v1_20_R2", configuration = "reobf"))
     implementation(project(path = ":eco-core:core-nms:v1_20_R3", configuration = "reobf"))
     implementation(project(path = ":eco-core:core-nms:v1_21", configuration = "reobf"))
+    implementation(project(path = ":eco-core:core-nms:v1_21_3", configuration = "reobf"))
+    implementation(project(path = ":eco-core:core-nms:v1_21_4", configuration = "reobf"))
+    implementation(project(path = ":eco-core:core-nms:v1_21_5", configuration = "reobf"))
+    implementation(project(path = ":eco-core:core-nms:v1_21_6", configuration = "reobf"))
 }
 
 allprojects {
     apply(plugin = "java")
     apply(plugin = "java-library")
     apply(plugin = "maven-publish")
-    apply(plugin = "io.github.goooler.shadow")
+    apply(plugin = "com.gradleup.shadow")
     apply(plugin = "kotlin")
 
     repositories {
         mavenCentral()
+
         maven("https://repo.auxilor.io/repository/maven-public/")
+
         maven("https://jitpack.io") {
             content { includeGroupByRegex("com\\.github\\..*") }
         }
 
+        // Paper
+        maven("https://repo.papermc.io/repository/maven-public/")
+
         // SuperiorSkyblock2
         maven("https://repo.bg-software.com/repository/api/")
 
@@ -102,12 +113,12 @@ allprojects {
 
     dependencies {
         // Kotlin
-        implementation(kotlin("stdlib", version = "1.9.21"))
+        implementation(kotlin("stdlib", version = "2.1.0"))
         implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.3")
 
         // Included in spigot jar, no need to move to implementation
         compileOnly("org.jetbrains:annotations:23.0.0")
-        compileOnly("com.google.guava:guava:31.1-jre")
+        compileOnly("com.google.guava:guava:32.0.0-jre")
 
         // Test
         testImplementation("org.junit.jupiter:junit-jupiter-api:5.9.2")
@@ -151,8 +162,8 @@ allprojects {
         }
 
         compileKotlin {
-            kotlinOptions {
+            compilerOptions {
-                jvmTarget = "17"
+                jvmTarget.set(JvmTarget.JVM_17)
             }
         }
 
@@ -175,14 +186,14 @@ allprojects {
         }
 
         withType<JavaCompile>().configureEach {
-            options.release = 17
+            options.release.set(17)
         }
     }
 
     java {
         withSourcesJar()
         toolchain {
-            languageVersion = JavaLanguageVersion.of(21)
+            languageVersion.set(JavaLanguageVersion.of(21))
         }
     }
 }
@@ -223,4 +234,4 @@ tasks {
 }
 
 group = "com.willfp"
-version = findProperty("version")!!
+version = findProperty("version")!!

eco-api/src/main/java/com/willfp/eco/core/EcoPlugin.java

@@ -37,8 +37,6 @@ import org.jetbrains.annotations.Nullable;
 import java.io.File;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collection;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;

eco-api/src/main/java/com/willfp/eco/core/Prerequisite.java

@@ -38,15 +38,23 @@ public class Prerequisite {
     );
 
     /**
-     * Requires the server to be running 1.21.
+     * Requires the server to be running at least 1.21.3.
+     */
+    public static final Prerequisite HAS_1_21_3 = new Prerequisite(
+            () -> ProxyConstants.NMS_VERSION.contains("1_21_3"),
+            "Requires server to be running 1.21.3+"
+    );
+
+    /**
+     * Requires the server to be running at least 1.21.
      */
     public static final Prerequisite HAS_1_21 = new Prerequisite(
-            () -> ProxyConstants.NMS_VERSION.contains("1_21"),
+            () -> ProxyConstants.NMS_VERSION.contains("1_21") || HAS_1_21_3.isMet(),
             "Requires server to be running 1.21+"
     );
 
     /**
-     * Requires the server to be running 1.20.5.
+     * Requires the server to be running at least 1.20.5.
      */
     public static final Prerequisite HAS_1_20_5 = new Prerequisite(
             () -> (ProxyConstants.NMS_VERSION.contains("1_20_") && !ProxyConstants.NMS_VERSION.contains("R"))
@@ -55,7 +63,7 @@ public class Prerequisite {
     );
 
     /**
-     * Requires the server to be running 1.20.3.
+     * Requires the server to be running at least 1.20.3.
      */
     public static final Prerequisite HAS_1_20_3 = new Prerequisite(
             () -> ProxyConstants.NMS_VERSION.contains("20_R3") || HAS_1_20_5.isMet(),
@@ -63,7 +71,7 @@ public class Prerequisite {
     );
 
     /**
-     * Requires the server to be running 1.20.
+     * Requires the server to be running at least 1.20.
      */
     public static final Prerequisite HAS_1_20 = new Prerequisite(
             () -> ProxyConstants.NMS_VERSION.contains("20") || HAS_1_20_3.isMet(),
@@ -71,7 +79,7 @@ public class Prerequisite {
     );
 
     /**
-     * Requires the server to be running 1.19.4.
+     * Requires the server to be running at least 1.19.4.
      */
     public static final Prerequisite HAS_1_19_4 = new Prerequisite(
             () -> ProxyConstants.NMS_VERSION.contains("19_R3") || HAS_1_20.isMet(),
@@ -79,7 +87,7 @@ public class Prerequisite {
     );
 
     /**
-     * Requires the server to be running 1.19.
+     * Requires the server to be running at least 1.19.
      */
     public static final Prerequisite HAS_1_19 = new Prerequisite(
             () -> ProxyConstants.NMS_VERSION.contains("19") || HAS_1_20.isMet(),
@@ -87,7 +95,7 @@ public class Prerequisite {
     );
 
     /**
-     * Requires the server to be running 1.18.
+     * Requires the server to be running at least 1.18.
      */
     public static final Prerequisite HAS_1_18 = new Prerequisite(
             () -> ProxyConstants.NMS_VERSION.contains("18") || HAS_1_19.isMet(),

eco-api/src/main/java/com/willfp/eco/core/data/handlers/PersistentDataHandler.java

@@ -6,7 +6,6 @@ import com.willfp.eco.core.tuples.Pair;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import java.util.HashMap;
 import java.util.Map;
 import java.util.Set;
 import java.util.UUID;

eco-api/src/main/java/com/willfp/eco/core/entities/Entities.java

@@ -111,6 +111,11 @@ public final class Entities {
             } catch (IllegalArgumentException e) {
                 return new EmptyTestableEntity();
             }
+
+            if (type.getEntityClass() == null) {
+                return new EmptyTestableEntity();
+            }
+
             entity = new SimpleTestableEntity(type);
         } else {
             String namespace = split[0];

eco-api/src/main/java/com/willfp/eco/core/entities/ai/entity/EntityGoalUseItem.java

@@ -6,6 +6,7 @@ import com.willfp.eco.core.entities.TestableEntity;
 import com.willfp.eco.core.entities.ai.EntityGoal;
 import com.willfp.eco.core.items.Items;
 import com.willfp.eco.core.serialization.KeyedDeserializer;
+import com.willfp.eco.util.SoundUtils;
 import org.bukkit.NamespacedKey;
 import org.bukkit.Sound;
 import org.bukkit.entity.LivingEntity;
@@ -50,9 +51,15 @@ public record EntityGoalUseItem(
 
             TestableEntity filter = Entities.lookup(config.getString("condition"));
 
+            Sound sound = SoundUtils.getSound(config.getString("sound"));
+
+            if (sound == null) {
+                return null;
+            }
+
             return new EntityGoalUseItem(
                     Items.lookup(config.getString("item")).getItem(),
-                    Sound.valueOf(config.getString("sound").toUpperCase()),
+                    sound,
                     filter::matches
             );
         }

eco-api/src/main/java/com/willfp/eco/core/entities/ai/target/TargetGoalNearestAttackable.java

@@ -11,7 +11,6 @@ import org.bukkit.entity.Raider;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import java.util.List;
 import java.util.Set;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;

eco-api/src/main/java/com/willfp/eco/core/integrations/antigrief/AntigriefManager.java

@@ -7,9 +7,6 @@ import org.bukkit.entity.LivingEntity;
 import org.bukkit.entity.Player;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.HashSet;
-import java.util.Set;
-
 /**
  * Class to handle antigrief integrations.
  */

eco-api/src/main/java/com/willfp/eco/core/integrations/customitems/CustomItemsManager.java

@@ -3,9 +3,6 @@ package com.willfp.eco.core.integrations.customitems;
 import com.willfp.eco.core.integrations.IntegrationRegistry;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.HashSet;
-import java.util.Set;
-
 /**
  * Class to handle custom item integrations.
  */

eco-api/src/main/java/com/willfp/eco/core/integrations/mcmmo/McmmoManager.java

@@ -5,9 +5,6 @@ import org.bukkit.block.Block;
 import org.bukkit.event.Event;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.HashSet;
-import java.util.Set;
-
 /**
  * Class to handle mcmmo integrations.
  */

eco-api/src/main/java/com/willfp/eco/core/packet/Packet.java

@@ -6,10 +6,51 @@ import org.jetbrains.annotations.NotNull;
 
 /**
  * Represents a packet.
- *
- * @param handle The NMS handle.
  */
-public record Packet(@NotNull Object handle) {
+public class Packet {
+    /**
+     * The packet handle.
+     */
+    private Object handle;
+
+    /**
+     * Create a new packet.
+     *
+     * @param handle The packet handle.
+     */
+    public Packet(@NotNull final Object handle) {
+        this.handle = handle;
+    }
+
+    /**
+     * Get the packet handle.
+     *
+     * @return The packet handle.
+     */
+    public Object getHandle() {
+        return handle;
+    }
+
+    /**
+     * Set the packet handle.
+     *
+     * @param handle The packet handle.
+     */
+    public void setHandle(@NotNull final Object handle) {
+        this.handle = handle;
+    }
+
+    /**
+     * Get the packet handle, compatible with the old record-based packet system.
+     *
+     * @return The packet handle.
+     * @deprecated Use {@link #getHandle()} instead.
+     */
+    @Deprecated
+    public Object handle() {
+        return handle;
+    }
+
     /**
      * Send to a player.
      *

eco-api/src/main/java/com/willfp/eco/core/proxy/ProxyConstants.java

@@ -29,7 +29,11 @@ public final class ProxyConstants {
             "v1_20_R1",
             "v1_20_R2",
             "v1_20_R3",
-            "v1_21"
+            "v1_21",
+            "v1_21_3",
+            "v1_21_4",
+            "v1_21_5",
+            "v1_21_6"
     );
 
     private ProxyConstants() {
@@ -39,6 +43,7 @@ public final class ProxyConstants {
     private static String convertVersion(@NotNull final String version) {
         return switch (version) {
             case "v1_21_1" -> "v1_21";
+            case "v1_21_2" -> "v1_21_3";
             default -> version;
         };
     }

eco-api/src/main/java/com/willfp/eco/core/sound/PlayableSound.java

@@ -2,6 +2,7 @@ package com.willfp.eco.core.sound;
 
 import com.willfp.eco.core.config.interfaces.Config;
 import com.willfp.eco.core.serialization.ConfigDeserializer;
+import com.willfp.eco.util.SoundUtils;
 import org.bukkit.Location;
 import org.bukkit.Sound;
 import org.bukkit.World;
@@ -82,20 +83,20 @@ public record PlayableSound(@NotNull Sound sound,
                 return null;
             }
 
-            try {
+            Sound sound = SoundUtils.getSound(config.getString("sound"));
-                Sound sound = Sound.valueOf(config.getString("sound").toUpperCase());
 
-                double pitch = Objects.requireNonNullElse(config.getDoubleOrNull("pitch"), 1.0);
+            if (sound == null) {
-                double volume = Objects.requireNonNullElse(config.getDoubleOrNull("volume"), 1.0);
-
-                return new PlayableSound(
-                        sound,
-                        pitch,
-                        volume
-                );
-            } catch (IllegalArgumentException e) {
                 return null;
             }
+
+            double pitch = Objects.requireNonNullElse(config.getDoubleOrNull("pitch"), 1.0);
+            double volume = Objects.requireNonNullElse(config.getDoubleOrNull("volume"), 1.0);
+
+            return new PlayableSound(
+                    sound,
+                    pitch,
+                    volume
+            );
         }
     }
 }

eco-api/src/main/java/com/willfp/eco/util/SoundUtils.java

@@ -0,0 +1,50 @@
+package com.willfp.eco.util;
+
+import com.willfp.eco.core.Prerequisite;
+import org.bukkit.NamespacedKey;
+import org.bukkit.Registry;
+import org.bukkit.Sound;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Field;
+
+/**
+ * Utilities / API methods for sounds.
+ */
+public final class SoundUtils {
+    /**
+     * Get a sound in a version-compatible way.
+     *
+     * @param name The name of the sound, case-insensitive.
+     * @return The sound, or null if not found.
+     */
+    @Nullable
+    public static Sound getSound(@NotNull final String name) {
+        if (!Prerequisite.HAS_1_21_3.isMet()) {
+            try {
+                return Sound.valueOf(name.toUpperCase());
+            } catch (IllegalArgumentException e) {
+                return null;
+            }
+        }
+
+        // First try from registry (preferred)
+        Sound fromRegistry = Registry.SOUNDS.get(NamespacedKey.minecraft(name.toLowerCase()));
+        if (fromRegistry != null) {
+            return fromRegistry;
+        }
+
+        // Next try using reflection (for legacy enum names)
+        try {
+            Field field = Sound.class.getDeclaredField(name.toUpperCase());
+            return (Sound) field.get(null);
+        } catch (ReflectiveOperationException e) {
+            return null;
+        }
+    }
+
+    private SoundUtils() {
+        throw new UnsupportedOperationException("This is a utility class and cannot be instantiated");
+    }
+}

eco-api/src/main/kotlin/com/willfp/eco/core/entities/Entities.kt

@@ -3,10 +3,7 @@
 package com.willfp.eco.core.entities
 
 import com.willfp.eco.core.entities.ai.EntityController
-import com.willfp.eco.core.items.Items
-import com.willfp.eco.core.items.TestableItem
 import org.bukkit.entity.Mob
-import org.bukkit.inventory.ItemStack
 
 /** @see EntityController.getFor */
 val <T : Mob> T.controller: EntityController<T>

eco-core/core-backend-modern/build.gradle.kts

@@ -1,3 +1,5 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 group = "com.willfp"
 version = rootProject.version
 
@@ -8,12 +10,12 @@ dependencies {
 
 tasks {
     compileJava {
-        options.release = 21
+        options.release.set(21)
     }
 
     compileKotlin {
-        kotlinOptions {
+        compilerOptions {
-            jvmTarget = "21"
+            jvmTarget.set(JvmTarget.JVM_21)
         }
     }
 }

eco-core/core-backend-modern/src/main/kotlin/com/willfp/eco/internal/compat/modern/entities/parsers/EntityArgParserScale.kt

@@ -4,8 +4,6 @@ import com.willfp.eco.core.entities.args.EntityArgParseResult
 import com.willfp.eco.core.entities.args.EntityArgParser
 import org.bukkit.attribute.Attribute
 import org.bukkit.entity.LivingEntity
-import org.bukkit.entity.Phantom
-import org.bukkit.entity.Slime
 
 object EntityArgParserScale : EntityArgParser {
     override fun parseArguments(args: Array<out String>): EntityArgParseResult? {

eco-core/core-backend/build.gradle.kts

@@ -1,3 +1,5 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 group = "com.willfp"
 version = rootProject.version
 
@@ -16,12 +18,12 @@ dependencies {
 
 tasks {
     compileJava {
-        options.release = 17
+        options.release.set(17)
     }
 
     compileKotlin {
-        kotlinOptions {
+        compilerOptions {
-            jvmTarget = "17"
+            jvmTarget.set(JvmTarget.JVM_17)
         }
     }
 }

eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/events/EcoEventManager.kt

@@ -9,7 +9,6 @@ import com.willfp.eco.core.packet.PacketPriority
 import org.bukkit.Bukkit
 import org.bukkit.event.HandlerList
 import org.bukkit.event.Listener
-import java.lang.Exception
 
 
 private class RegisteredPacketListener(
@@ -80,9 +79,11 @@ class EcoEventManager(private val plugin: EcoPlugin) : EventManager {
     }
 
     override fun registerPacketListener(listener: PacketListener) {
-        listeners[listener.priority] += RegisteredPacketListener(
+        listeners[listener.priority].add(
-            plugin,
+            RegisteredPacketListener(
-            listener
+                plugin,
+                listener
+            )
         )
     }
 }

eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoSlotBuilder.kt

@@ -23,7 +23,7 @@ class EcoSlotBuilder(private val provider: SlotProvider) : SlotBuilder {
     private var notCaptiveFor: (Player) -> Boolean = { _ -> false}
 
     override fun onClick(type: ClickType, action: SlotHandler): SlotBuilder {
-        handlers[type] += action
+        handlers[type].add(action)
         return this
     }
 

eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/items/ArgParserName.kt

@@ -2,9 +2,7 @@ package com.willfp.eco.internal.items
 
 import com.willfp.eco.internal.items.templates.ValueArgParser
 import com.willfp.eco.util.StringUtils
-import org.bukkit.inventory.ItemStack
 import org.bukkit.inventory.meta.ItemMeta
-import java.util.function.Predicate
 
 object ArgParserName : ValueArgParser<String>("name") {
     override fun parse(arg: String): String {

eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/items/templates/ValueArgParser.kt

@@ -1,7 +1,6 @@
 package com.willfp.eco.internal.items.templates
 
 import com.willfp.eco.core.items.args.LookupArgParser
-import com.willfp.eco.util.StringUtils
 import org.bukkit.inventory.ItemStack
 import org.bukkit.inventory.meta.ItemMeta
 import java.util.function.Predicate

eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/proxy/EcoProxyFactory.kt

@@ -50,8 +50,7 @@ class EcoProxyFactory(
             )
         } else {
             ProxyError(
-                "Could not initialize proxy. If you're seeing this error message"
+                "Could not initialize proxy. Are you running a supported server version?",
-                        + ", something has gone badly wrong. This almost definitely isn't user error, blame the developer.",
                 e
             )
         }

eco-core/core-nms/build.gradle.kts

@@ -1,5 +1,5 @@
 plugins {
-    id("io.papermc.paperweight.userdev") version "1.7.1" apply false
+    id("io.papermc.paperweight.userdev") version "2.0.0-beta.17" apply false
 }
 
 

eco-core/core-nms/common/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/common/ai/entity/RangedBowAttackGoalFactory.kt

@@ -10,7 +10,7 @@ import net.minecraft.world.entity.monster.RangedAttackMob
 
 object RangedBowAttackGoalFactory : EntityGoalFactory<EntityGoalRangedBowAttack> {
     override fun create(apiGoal: EntityGoalRangedBowAttack, entity: PathfinderMob): Goal? {
-        (if (entity !is Monster) return null)
+        if (entity !is Monster) return null
         if (entity !is RangedAttackMob) return null
 
         return RangedBowAttackGoal(

eco-core/core-nms/common/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/common/ai/entity/RangedCrossbowAttackGoalFactory.kt

@@ -11,7 +11,7 @@ import net.minecraft.world.entity.monster.RangedAttackMob
 
 object RangedCrossbowAttackGoalFactory : EntityGoalFactory<EntityGoalRangedCrossbowAttack> {
     override fun create(apiGoal: EntityGoalRangedCrossbowAttack, entity: PathfinderMob): Goal? {
-        (if (entity !is Monster) return null)
+        if (entity !is Monster) return null
         if (entity !is RangedAttackMob) return null
         if (entity !is CrossbowAttackMob) return null
 

eco-core/core-nms/common/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/common/ai/target/NearestAttackableGoalFactory.kt

@@ -1,7 +1,6 @@
 package com.willfp.eco.internal.spigot.proxy.common.ai.target
 
 import com.willfp.eco.core.entities.ai.target.TargetGoalNearestAttackable
-import com.willfp.eco.core.lookup.matches
 import com.willfp.eco.internal.spigot.proxy.common.ai.TargetGoalFactory
 import com.willfp.eco.internal.spigot.proxy.common.toBukkitEntity
 import net.minecraft.world.entity.LivingEntity

eco-core/core-nms/common/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/common/packet/EcoChannelDuplexHandler.kt

@@ -23,7 +23,7 @@ class EcoChannelDuplexHandler(
             event.handleReceive()
 
             if (!event.isCancelled) {
-                super.channelRead(ctx, msg)
+                super.channelRead(ctx, event.packet.handle)
             }
         } else {
             super.channelRead(ctx, msg)
@@ -39,7 +39,7 @@ class EcoChannelDuplexHandler(
             event.handleSend()
 
             if (!event.isCancelled) {
-                super.write(ctx, msg, promise)
+                super.write(ctx, event.packet.handle, promise)
             }
         } else {
             super.write(ctx, msg, promise)

eco-core/core-nms/common/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/common/packet/display/PacketWindowItems.kt

@@ -15,7 +15,7 @@ import org.bukkit.inventory.ItemStack
 import java.util.UUID
 import java.util.concurrent.ConcurrentHashMap
 
-class PacketWindowItems(
+open class PacketWindowItems(
     private val plugin: EcoPlugin
 ) : PacketListener {
     private val lastKnownWindowIDs = ConcurrentHashMap<UUID, Int>()
@@ -52,7 +52,7 @@ class PacketWindowItems(
     }
 
 
-    private fun modifyWindowItems(
+    protected fun modifyWindowItems(
         itemStacks: MutableList<ItemStack>,
         windowId: Int,
         player: Player

eco-core/core-nms/modern/build.gradle.kts

@@ -1,3 +1,5 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 plugins {
     id("io.papermc.paperweight.userdev")
 }
@@ -12,12 +14,12 @@ dependencies {
 
 tasks {
     compileJava {
-        options.release = 21
+        options.release.set(21)
     }
 
     compileKotlin {
-        kotlinOptions {
+        compilerOptions {
-            jvmTarget = "21"
+            jvmTarget.set(JvmTarget.JVM_21)
         }
     }
 }

eco-core/core-nms/modern/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/common/modern/NewEcoFastItemStack.kt

@@ -14,8 +14,6 @@ import com.willfp.eco.util.StringUtils
 import com.willfp.eco.util.toComponent
 import com.willfp.eco.util.toLegacy
 import net.kyori.adventure.text.Component
-import net.kyori.adventure.text.format.Style
-import net.kyori.adventure.text.format.TextColor
 import net.kyori.adventure.text.format.TextDecoration
 import net.minecraft.core.component.DataComponentType
 import net.minecraft.core.component.DataComponents
@@ -23,12 +21,9 @@ import net.minecraft.core.registries.Registries
 import net.minecraft.nbt.CompoundTag
 import net.minecraft.util.Unit
 import net.minecraft.world.item.component.CustomData
-import net.minecraft.world.item.component.CustomModelData
 import net.minecraft.world.item.component.ItemLore
 import net.minecraft.world.item.enchantment.ItemEnchantments
-import org.bukkit.Bukkit
 import org.bukkit.craftbukkit.CraftRegistry
-import org.bukkit.craftbukkit.CraftServer
 import org.bukkit.craftbukkit.enchantments.CraftEnchantment
 import org.bukkit.enchantments.Enchantment
 import org.bukkit.inventory.ItemFlag
@@ -44,12 +39,12 @@ private fun Component.unstyled(): Component {
     return unstyledComponent.append(this)
 }
 
-class NewEcoFastItemStack(
+open class NewEcoFastItemStack(
-    private val bukkit: ItemStack
+    private val bukkit: ItemStack,
 ) : ImplementedFIS {
     // Cast is there because, try as I might, I can't get IntellIJ to recognise half the classes in the dev bundle
     @Suppress("USELESS_CAST")
-    private val handle = bukkit.asNMSStack() as net.minecraft.world.item.ItemStack
+    protected val handle = bukkit.asNMSStack() as net.minecraft.world.item.ItemStack
 
     private val pdc = (handle.get(DataComponents.CUSTOM_DATA)?.copyTag() ?: CompoundTag()).makePdc()
 
@@ -81,22 +76,17 @@ class NewEcoFastItemStack(
         enchantment: Enchantment,
         checkStored: Boolean
     ): Int {
-        val minecraft =
+        val minecraft = CraftRegistry.bukkitToMinecraftHolder(
-            CraftRegistry.bukkitToMinecraft<Enchantment, net.minecraft.world.item.enchantment.Enchantment>(
+            enchantment,
-                enchantment
+            Registries.ENCHANTMENT
-            )
+        )
-
-        val server = Bukkit.getServer() as CraftServer
-        val access = server.server.registryAccess()
-
-        val holder = access.registryOrThrow(Registries.ENCHANTMENT).wrapAsHolder(minecraft)
 
         val enchantments = handle.get(DataComponents.ENCHANTMENTS) ?: return 0
-        var level = enchantments.getLevel(holder)
+        var level = enchantments.getLevel(minecraft)
 
         if (checkStored) {
             val storedEnchantments = handle.get(DataComponents.STORED_ENCHANTMENTS) ?: return 0
-            level = max(level, storedEnchantments.getLevel(holder))
+            level = max(level, storedEnchantments.getLevel(minecraft))
         }
 
         return level
@@ -154,7 +144,7 @@ class NewEcoFastItemStack(
 
     override fun getDisplayName(): String = displayNameComponent.toLegacy()
 
-    private fun <T> net.minecraft.world.item.ItemStack.modifyComponent(
+    protected fun <T> net.minecraft.world.item.ItemStack.modifyComponent(
         component: DataComponentType<T>,
         modifier: (T) -> T
     ) {
@@ -369,19 +359,23 @@ class NewEcoFastItemStack(
 
     override fun getType(): org.bukkit.Material = handle.getItem().toMaterial()
 
+    /*
+    Custom model data doesn't work based on an integer since 1.21.3, so these methods do nothing
+     */
+
     override fun getCustomModelData(): Int? =
-        handle.get(DataComponents.CUSTOM_MODEL_DATA)?.value
+        null
 
     override fun setCustomModelData(data: Int?) {
         if (data == null) {
             handle.remove(DataComponents.CUSTOM_MODEL_DATA)
-        } else {
-            handle.set(DataComponents.CUSTOM_MODEL_DATA, CustomModelData(data))
         }
 
         apply()
     }
 
+    // END
+
     override fun equals(other: Any?): Boolean {
         if (other !is NewEcoFastItemStack) {
             return false

eco-core/core-nms/v1_17_R1/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_17_R1/ExtendedPersistentDataContainerFactory.kt

@@ -2,7 +2,6 @@ package com.willfp.eco.internal.spigot.proxy.v1_17_R1
 
 import com.willfp.eco.core.data.ExtendedPersistentDataContainer
 import com.willfp.eco.internal.spigot.proxy.ExtendedPersistentDataContainerFactoryProxy
-import com.willfp.eco.internal.spigot.proxy.common.item.ContinuallyAppliedPersistentDataContainer
 import net.minecraft.nbt.Tag
 import org.bukkit.Material
 import org.bukkit.craftbukkit.v1_17_R1.inventory.CraftItemStack

eco-core/core-nms/v1_18_R1/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_18_R1/ExtendedPersistentDataContainerFactory.kt

@@ -2,7 +2,6 @@ package com.willfp.eco.internal.spigot.proxy.v1_18_R1
 
 import com.willfp.eco.core.data.ExtendedPersistentDataContainer
 import com.willfp.eco.internal.spigot.proxy.ExtendedPersistentDataContainerFactoryProxy
-import com.willfp.eco.internal.spigot.proxy.common.item.ContinuallyAppliedPersistentDataContainer
 import net.minecraft.nbt.Tag
 import org.bukkit.Material
 import org.bukkit.craftbukkit.v1_18_R1.inventory.CraftItemStack

eco-core/core-nms/v1_18_R2/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_18_R2/ExtendedPersistentDataContainerFactory.kt

@@ -2,7 +2,6 @@ package com.willfp.eco.internal.spigot.proxy.v1_18_R2
 
 import com.willfp.eco.core.data.ExtendedPersistentDataContainer
 import com.willfp.eco.internal.spigot.proxy.ExtendedPersistentDataContainerFactoryProxy
-import com.willfp.eco.internal.spigot.proxy.common.item.ContinuallyAppliedPersistentDataContainer
 import net.minecraft.nbt.Tag
 import org.bukkit.Material
 import org.bukkit.craftbukkit.v1_18_R2.inventory.CraftItemStack

eco-core/core-nms/v1_19_R1/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_19_R1/SNBTConverter.kt

@@ -3,7 +3,6 @@ package com.willfp.eco.internal.spigot.proxy.v1_19_R1
 import com.willfp.eco.core.items.TestableItem
 import com.willfp.eco.core.recipe.parts.EmptyTestableItem
 import com.willfp.eco.internal.spigot.proxy.SNBTConverterProxy
-import com.willfp.eco.internal.spigot.proxy.common.toMaterial
 import net.minecraft.nbt.CompoundTag
 import net.minecraft.nbt.SnbtPrinterTagVisitor
 import net.minecraft.nbt.TagParser

eco-core/core-nms/v1_19_R2/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_19_R2/CommonsInitializer.kt

@@ -5,7 +5,6 @@ import com.willfp.eco.internal.spigot.proxy.CommonsInitializerProxy
 import com.willfp.eco.internal.spigot.proxy.common.CommonsProvider
 import com.willfp.eco.internal.spigot.proxy.common.packet.PacketInjectorListener
 import com.willfp.eco.internal.spigot.proxy.common.toResourceLocation
-import io.netty.channel.Channel
 import net.kyori.adventure.text.Component
 import net.kyori.adventure.text.serializer.gson.GsonComponentSerializer
 import net.minecraft.core.registries.BuiltInRegistries
@@ -13,7 +12,6 @@ import net.minecraft.nbt.CompoundTag
 import net.minecraft.nbt.Tag
 import net.minecraft.resources.ResourceLocation
 import net.minecraft.server.level.ServerPlayer
-import net.minecraft.server.network.ServerGamePacketListenerImpl
 import net.minecraft.world.entity.PathfinderMob
 import net.minecraft.world.item.Item
 import org.bukkit.Bukkit

eco-core/core-nms/v1_19_R2/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_19_R2/ExtendedPersistentDataContainerFactory.kt

@@ -2,7 +2,6 @@ package com.willfp.eco.internal.spigot.proxy.v1_19_R2
 
 import com.willfp.eco.core.data.ExtendedPersistentDataContainer
 import com.willfp.eco.internal.spigot.proxy.ExtendedPersistentDataContainerFactoryProxy
-import com.willfp.eco.internal.spigot.proxy.common.item.ContinuallyAppliedPersistentDataContainer
 import net.minecraft.nbt.Tag
 import org.bukkit.Material
 import org.bukkit.craftbukkit.v1_19_R2.inventory.CraftItemStack

eco-core/core-nms/v1_20_R1/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_20_R1/DisplayName.kt

@@ -4,7 +4,6 @@ import com.willfp.eco.core.packet.Packet
 import com.willfp.eco.core.packet.sendPacket
 import com.willfp.eco.internal.spigot.proxy.DisplayNameProxy
 import com.willfp.eco.internal.spigot.proxy.common.toNMS
-import io.papermc.paper.adventure.PaperAdventure
 import net.kyori.adventure.text.Component
 import net.minecraft.network.protocol.game.ClientboundSetEntityDataPacket
 import net.minecraft.network.syncher.EntityDataAccessor

eco-core/core-nms/v1_20_R2/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_20_R2/DisplayName.kt

@@ -4,16 +4,13 @@ import com.willfp.eco.core.packet.Packet
 import com.willfp.eco.core.packet.sendPacket
 import com.willfp.eco.internal.spigot.proxy.DisplayNameProxy
 import com.willfp.eco.internal.spigot.proxy.common.toNMS
-import io.papermc.paper.adventure.PaperAdventure
 import net.kyori.adventure.text.Component
 import net.minecraft.network.protocol.game.ClientboundSetEntityDataPacket
 import net.minecraft.network.syncher.EntityDataAccessor
 import net.minecraft.network.syncher.SynchedEntityData
 import net.minecraft.world.entity.Entity
 import org.bukkit.craftbukkit.v1_20_R2.entity.CraftLivingEntity
-import org.bukkit.craftbukkit.v1_20_R2.entity.CraftMob
 import org.bukkit.entity.LivingEntity
-import org.bukkit.entity.Mob
 import org.bukkit.entity.Player
 import java.util.Optional
 

eco-core/core-nms/v1_20_R3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_20_R3/DisplayName.kt

@@ -4,16 +4,13 @@ import com.willfp.eco.core.packet.Packet
 import com.willfp.eco.core.packet.sendPacket
 import com.willfp.eco.internal.spigot.proxy.DisplayNameProxy
 import com.willfp.eco.internal.spigot.proxy.common.toNMS
-import io.papermc.paper.adventure.PaperAdventure
 import net.kyori.adventure.text.Component
 import net.minecraft.network.protocol.game.ClientboundSetEntityDataPacket
 import net.minecraft.network.syncher.EntityDataAccessor
 import net.minecraft.network.syncher.SynchedEntityData
 import net.minecraft.world.entity.Entity
 import org.bukkit.craftbukkit.v1_20_R3.entity.CraftLivingEntity
-import org.bukkit.craftbukkit.v1_20_R3.entity.CraftMob
 import org.bukkit.entity.LivingEntity
-import org.bukkit.entity.Mob
 import org.bukkit.entity.Player
 import java.util.Optional
 

eco-core/core-nms/v1_20_R3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_20_R3/DummyEntityFactory.kt

@@ -5,7 +5,6 @@ import com.willfp.eco.internal.spigot.proxy.DummyEntityFactoryProxy
 import org.bukkit.Location
 import org.bukkit.craftbukkit.v1_20_R3.CraftWorld
 import org.bukkit.entity.Entity
-import org.bukkit.entity.EntityType
 import org.bukkit.entity.Zombie
 
 class DummyEntityFactory : DummyEntityFactoryProxy {

eco-core/core-nms/v1_20_R3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_20_R3/ExtendedPersistentDataContainerFactory.kt

@@ -2,7 +2,6 @@ package com.willfp.eco.internal.spigot.proxy.v1_20_R3
 
 import com.willfp.eco.core.data.ExtendedPersistentDataContainer
 import com.willfp.eco.internal.spigot.proxy.ExtendedPersistentDataContainerFactoryProxy
-import com.willfp.eco.internal.spigot.proxy.common.item.ContinuallyAppliedPersistentDataContainer
 import net.minecraft.nbt.Tag
 import org.bukkit.Material
 import org.bukkit.craftbukkit.v1_20_R3.inventory.CraftItemStack

eco-core/core-nms/v1_21/build.gradle.kts

@@ -1,3 +1,5 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 plugins {
     id("io.papermc.paperweight.userdev")
 }
@@ -39,12 +41,12 @@ tasks {
     }
 
     compileJava {
-        options.release = 21
+        options.release.set(21)
     }
 
     compileKotlin {
-        kotlinOptions {
+        compilerOptions {
-            jvmTarget = "21"
+            jvmTarget.set(JvmTarget.JVM_21)
         }
     }
 }

eco-core/core-nms/v1_21/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21/FastItemStackFactory.kt

@@ -3,10 +3,29 @@ package com.willfp.eco.internal.spigot.proxy.v1_21
 import com.willfp.eco.core.fast.FastItemStack
 import com.willfp.eco.internal.spigot.proxy.FastItemStackFactoryProxy
 import com.willfp.eco.internal.spigot.proxy.common.modern.NewEcoFastItemStack
+import net.minecraft.core.component.DataComponents
+import net.minecraft.world.item.component.CustomModelData
 import org.bukkit.inventory.ItemStack
 
 class FastItemStackFactory : FastItemStackFactoryProxy {
     override fun create(itemStack: ItemStack): FastItemStack {
-        return NewEcoFastItemStack(itemStack)
+        return LegacyNewEcoFastItemStack(itemStack)
+    }
+
+    private class LegacyNewEcoFastItemStack(itemStack: ItemStack) :
+        NewEcoFastItemStack(itemStack) {
+
+        override fun getCustomModelData(): Int? =
+            handle.get(DataComponents.CUSTOM_MODEL_DATA)?.value
+
+        override fun setCustomModelData(data: Int?) {
+            if (data == null) {
+                handle.remove(DataComponents.CUSTOM_MODEL_DATA)
+            } else {
+                handle.set(DataComponents.CUSTOM_MODEL_DATA, CustomModelData(data))
+            }
+
+            apply()
+        }
     }
 }

eco-core/core-nms/v1_21_3/build.gradle.kts

@@ -0,0 +1,52 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
+plugins {
+    id("io.papermc.paperweight.userdev")
+}
+
+group = "com.willfp"
+version = rootProject.version
+
+dependencies {
+    implementation(project(":eco-core:core-nms:modern"))
+    implementation(project(":eco-core:core-nms:common"))
+    paperweight.paperDevBundle("1.21.3-R0.1-SNAPSHOT")
+
+    implementation("net.kyori:adventure-text-minimessage:4.11.0") {
+        version {
+            strictly("4.11.0")
+        }
+        exclude(group = "net.kyori", module = "adventure-api")
+    }
+}
+
+tasks {
+    build {
+        dependsOn(reobfJar)
+    }
+
+    reobfJar {
+        mustRunAfter(shadowJar)
+    }
+
+    shadowJar {
+        relocate(
+            "com.willfp.eco.internal.spigot.proxy.common",
+            "com.willfp.eco.internal.spigot.proxy.v1_21_3.common"
+        )
+        relocate(
+            "net.kyori.adventure.text.minimessage",
+            "com.willfp.eco.internal.spigot.proxy.v1_21_3.minimessage"
+        )
+    }
+
+    compileJava {
+        options.release.set(21)
+    }
+
+    compileKotlin {
+        compilerOptions {
+            jvmTarget.set(JvmTarget.JVM_21)
+        }
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/BukkitCommands.kt

@@ -0,0 +1,35 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.core.command.PluginCommandBase
+import com.willfp.eco.internal.spigot.proxy.BukkitCommandsProxy
+import org.bukkit.Bukkit
+import org.bukkit.command.Command
+import org.bukkit.command.SimpleCommandMap
+import org.bukkit.craftbukkit.CraftServer
+import java.lang.reflect.Field
+
+class BukkitCommands : BukkitCommandsProxy {
+    private val knownCommandsField: Field by lazy {
+        SimpleCommandMap::class.java.getDeclaredField("knownCommands")
+            .apply {
+                isAccessible = true
+            }
+    }
+
+    @Suppress("UNCHECKED_CAST")
+    private val knownCommands: MutableMap<String, Command>
+        get() = knownCommandsField.get(getCommandMap()) as MutableMap<String, Command>
+
+    override fun getCommandMap(): SimpleCommandMap {
+        return (Bukkit.getServer() as CraftServer).commandMap
+    }
+
+    override fun syncCommands() {
+        (Bukkit.getServer() as CraftServer).syncCommands()
+    }
+
+    override fun unregisterCommand(command: PluginCommandBase) {
+        knownCommands.remove(command.name)
+        knownCommands.remove("${command.plugin.name.lowercase()}:${command.name}")
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/CommonsInitializer.kt

@@ -0,0 +1,171 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.core.EcoPlugin
+import com.willfp.eco.internal.spigot.proxy.CommonsInitializerProxy
+import com.willfp.eco.internal.spigot.proxy.common.CommonsProvider
+import com.willfp.eco.internal.spigot.proxy.common.packet.PacketInjectorListener
+import com.willfp.eco.internal.spigot.proxy.common.toResourceLocation
+import net.kyori.adventure.text.Component
+import net.kyori.adventure.text.serializer.json.JSONComponentSerializer
+import net.minecraft.core.component.DataComponents
+import net.minecraft.core.registries.BuiltInRegistries
+import net.minecraft.nbt.CompoundTag
+import net.minecraft.nbt.Tag
+import net.minecraft.resources.ResourceLocation
+import net.minecraft.server.level.ServerPlayer
+import net.minecraft.world.entity.PathfinderMob
+import net.minecraft.world.item.Item
+import org.bukkit.Bukkit
+import org.bukkit.Material
+import org.bukkit.NamespacedKey
+import org.bukkit.craftbukkit.CraftServer
+import org.bukkit.craftbukkit.entity.CraftEntity
+import org.bukkit.craftbukkit.entity.CraftMob
+import org.bukkit.craftbukkit.entity.CraftPlayer
+import org.bukkit.craftbukkit.inventory.CraftItemStack
+import org.bukkit.craftbukkit.inventory.CraftMetaArmor
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataContainer
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataTypeRegistry
+import org.bukkit.craftbukkit.util.CraftMagicNumbers
+import org.bukkit.craftbukkit.util.CraftNamespacedKey
+import org.bukkit.entity.LivingEntity
+import org.bukkit.entity.Mob
+import org.bukkit.entity.Player
+import org.bukkit.inventory.ItemStack
+import org.bukkit.persistence.PersistentDataContainer
+import java.lang.reflect.Field
+
+class CommonsInitializer : CommonsInitializerProxy {
+    override fun init(plugin: EcoPlugin) {
+        CommonsProvider.setIfNeeded(CommonsProviderImpl)
+        plugin.onEnable {
+            plugin.eventManager.registerListener(PacketInjectorListener)
+        }
+    }
+
+    object CommonsProviderImpl : CommonsProvider {
+        private val cisHandle: Field = CraftItemStack::class.java.getDeclaredField("handle").apply {
+            isAccessible = true
+        }
+
+        private val pdcRegsitry = CraftMetaArmor::class.java
+            .superclass // Access CraftMetaItem
+            .getDeclaredField("DATA_TYPE_REGISTRY")
+            .apply { isAccessible = true }
+            .get(null) as CraftPersistentDataTypeRegistry
+
+        override val nbtTagString = CraftMagicNumbers.NBT.TAG_STRING
+
+        override fun toPathfinderMob(mob: Mob): PathfinderMob? {
+            val craft = mob as? CraftMob ?: return null
+            return craft.handle as? PathfinderMob
+        }
+
+        override fun toResourceLocation(namespacedKey: NamespacedKey): ResourceLocation =
+            CraftNamespacedKey.toMinecraft(namespacedKey)
+
+        override fun asNMSStack(itemStack: ItemStack): net.minecraft.world.item.ItemStack {
+            return if (itemStack !is CraftItemStack) {
+                CraftItemStack.asNMSCopy(itemStack)
+            } else {
+                cisHandle[itemStack] as net.minecraft.world.item.ItemStack? ?: CraftItemStack.asNMSCopy(itemStack)
+            }
+        }
+
+        override fun asBukkitStack(itemStack: net.minecraft.world.item.ItemStack): ItemStack {
+            return CraftItemStack.asCraftMirror(itemStack)
+        }
+
+        override fun mergeIfNeeded(itemStack: ItemStack, nmsStack: net.minecraft.world.item.ItemStack) {
+            if (itemStack !is CraftItemStack) {
+                itemStack.itemMeta = CraftItemStack.asCraftMirror(nmsStack).itemMeta
+            }
+        }
+
+        override fun toBukkitEntity(entity: net.minecraft.world.entity.LivingEntity): LivingEntity? =
+            CraftEntity.getEntity(Bukkit.getServer() as CraftServer, entity) as? LivingEntity
+
+        override fun makePdc(tag: CompoundTag, base: Boolean): PersistentDataContainer {
+            fun emptyPdc(): CraftPersistentDataContainer = CraftPersistentDataContainer(pdcRegsitry)
+
+            fun CompoundTag?.toPdc(): PersistentDataContainer {
+                val pdc = emptyPdc()
+                this ?: return pdc
+                val keys = this.allKeys
+                for (key in keys) {
+                    pdc.put(key, this[key])
+                }
+
+                return pdc
+            }
+
+            return if (base) {
+                tag.toPdc()
+            } else {
+                if (tag.contains("PublicBukkitValues")) {
+                    tag.getCompound("PublicBukkitValues").toPdc()
+                } else {
+                    emptyPdc()
+                }
+            }
+        }
+
+        override fun setPdc(
+            tag: CompoundTag,
+            pdc: PersistentDataContainer?,
+            item: net.minecraft.world.item.ItemStack?
+        ) {
+            fun CraftPersistentDataContainer.toTag(): CompoundTag {
+                val compound = CompoundTag()
+                val rawPublicMap: Map<String, Tag> = this.raw
+                for ((key, value) in rawPublicMap) {
+                    compound.put(key, value)
+                }
+
+                return compound
+            }
+
+            val container = when (pdc) {
+                is CraftPersistentDataContainer? -> pdc
+                else -> null
+            }
+
+            if (item != null) {
+                if (container != null && !container.isEmpty) {
+                    for (key in tag.allKeys.toSet()) {
+                        tag.remove(key)
+                    }
+
+                    tag.merge(container.toTag())
+                } else {
+                    item.remove(DataComponents.CUSTOM_DATA)
+                }
+            } else {
+                if (container != null && !container.isEmpty) {
+                    tag.put("PublicBukkitValues", container.toTag())
+                } else {
+                    tag.remove("PublicBukkitValues")
+                }
+            }
+        }
+
+        override fun materialToItem(material: Material): Item =
+            BuiltInRegistries.ITEM.getOptional(material.key.toResourceLocation())
+                .orElseThrow { IllegalArgumentException("Material is not item!") }
+
+        override fun itemToMaterial(item: Item) =
+            Material.getMaterial(BuiltInRegistries.ITEM.getKey(item).path.uppercase())
+                ?: throw IllegalArgumentException("Invalid material!")
+
+        override fun toNMS(player: Player): ServerPlayer {
+            return (player as CraftPlayer).handle
+        }
+
+        override fun toNMS(component: Component): net.minecraft.network.chat.Component {
+            val json = JSONComponentSerializer.json().serialize(component)
+            val holderLookupProvider = (Bukkit.getServer() as CraftServer).server.registryAccess()
+
+            return net.minecraft.network.chat.Component.Serializer.fromJson(json, holderLookupProvider)!!
+        }
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/DisplayName.kt

@@ -0,0 +1,57 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.core.packet.Packet
+import com.willfp.eco.core.packet.sendPacket
+import com.willfp.eco.internal.spigot.proxy.DisplayNameProxy
+import com.willfp.eco.internal.spigot.proxy.common.toNMS
+import net.kyori.adventure.text.Component
+import net.minecraft.network.protocol.game.ClientboundSetEntityDataPacket
+import net.minecraft.network.syncher.EntityDataAccessor
+import net.minecraft.network.syncher.SynchedEntityData
+import net.minecraft.world.entity.Entity
+import org.bukkit.craftbukkit.entity.CraftLivingEntity
+import org.bukkit.entity.LivingEntity
+import org.bukkit.entity.Player
+import java.util.Optional
+
+@Suppress("UNCHECKED_CAST")
+class DisplayName : DisplayNameProxy {
+    private val displayNameAccessor = Entity::class.java
+        .declaredFields
+        .filter { it.type == EntityDataAccessor::class.java }
+        .toList()[2]
+        .apply { isAccessible = true }
+        .get(null) as EntityDataAccessor<Optional<net.minecraft.network.chat.Component>>
+
+    private val customNameVisibleAccessor = Entity::class.java
+        .declaredFields
+        .filter { it.type == EntityDataAccessor::class.java }
+        .toList()[3]
+        .apply { isAccessible = true }
+        .get(null) as EntityDataAccessor<Boolean>
+
+    override fun setClientsideDisplayName(
+        entity: LivingEntity,
+        player: Player,
+        displayName: Component,
+        visible: Boolean
+    ) {
+        if (entity !is CraftLivingEntity) {
+            return
+        }
+
+        val nmsComponent = displayName.toNMS()
+
+        val nmsEntity = entity.handle
+
+        val packet = ClientboundSetEntityDataPacket(
+            nmsEntity.id,
+            listOf(
+                SynchedEntityData.DataValue.create(displayNameAccessor, Optional.of(nmsComponent)),
+                SynchedEntityData.DataValue.create(customNameVisibleAccessor, visible)
+            )
+        )
+
+        player.sendPacket(Packet(packet))
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/DummyEntityFactory.kt

@@ -0,0 +1,15 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.internal.entities.EcoDummyEntity
+import com.willfp.eco.internal.spigot.proxy.DummyEntityFactoryProxy
+import org.bukkit.Location
+import org.bukkit.craftbukkit.CraftWorld
+import org.bukkit.entity.Entity
+import org.bukkit.entity.Zombie
+
+class DummyEntityFactory : DummyEntityFactoryProxy {
+    override fun createDummyEntity(location: Location): Entity {
+        val world = location.world as CraftWorld
+        return EcoDummyEntity(world.createEntity(location, Zombie::class.java))
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/EntityControllerFactory.kt

@@ -0,0 +1,12 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.core.entities.ai.EntityController
+import com.willfp.eco.internal.spigot.proxy.EntityControllerFactoryProxy
+import com.willfp.eco.internal.spigot.proxy.v1_21_3.entity.EcoEntityController
+import org.bukkit.entity.Mob
+
+class EntityControllerFactory : EntityControllerFactoryProxy {
+    override fun <T : Mob> createEntityController(entity: T): EntityController<T> {
+        return EcoEntityController(entity)
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/ExtendedPersistentDataContainerFactory.kt

@@ -0,0 +1,91 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.core.data.ExtendedPersistentDataContainer
+import com.willfp.eco.internal.spigot.proxy.ExtendedPersistentDataContainerFactoryProxy
+import net.minecraft.nbt.Tag
+import org.bukkit.Material
+import org.bukkit.craftbukkit.inventory.CraftItemStack
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataContainer
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataTypeRegistry
+import org.bukkit.inventory.ItemStack
+import org.bukkit.persistence.PersistentDataContainer
+import org.bukkit.persistence.PersistentDataType
+import java.lang.reflect.Field
+
+class ExtendedPersistentDataContainerFactory : ExtendedPersistentDataContainerFactoryProxy {
+    private val registry: CraftPersistentDataTypeRegistry
+
+    init {
+        /*
+         Can't grab actual instance since it's in CraftMetaItem (which is package-private)
+         And getting it would mean more janky reflection
+         */
+        val item = CraftItemStack.asCraftCopy(ItemStack(Material.STONE))
+        val pdc = item.itemMeta!!.persistentDataContainer
+
+        // Cross-version compatibility:
+        val registryField: Field = try {
+            CraftPersistentDataContainer::class.java.getDeclaredField("registry")
+        } catch (e: NoSuchFieldException) {
+            CraftPersistentDataContainer::class.java.superclass.getDeclaredField("registry")
+        }
+
+        this.registry = registryField
+            .apply { isAccessible = true }.get(pdc) as CraftPersistentDataTypeRegistry
+    }
+
+    override fun adapt(pdc: PersistentDataContainer): ExtendedPersistentDataContainer {
+        return when (pdc) {
+            is CraftPersistentDataContainer -> EcoPersistentDataContainer(pdc)
+            else -> throw IllegalArgumentException("Custom PDC instance ${pdc::class.java.name} is not supported!")
+        }
+    }
+
+    override fun newPdc(): PersistentDataContainer {
+        return CraftPersistentDataContainer(registry)
+    }
+
+    inner class EcoPersistentDataContainer(
+        private val handle: CraftPersistentDataContainer
+    ) : ExtendedPersistentDataContainer {
+        @Suppress("UNCHECKED_CAST")
+        private val customDataTags: MutableMap<String, Tag> =
+            CraftPersistentDataContainer::class.java.getDeclaredField("customDataTags")
+                .apply { isAccessible = true }.get(handle) as MutableMap<String, Tag>
+
+        override fun <T : Any, Z : Any> set(key: String, dataType: PersistentDataType<T, Z>, value: Z) {
+            customDataTags[key] =
+                registry.wrap(dataType, dataType.toPrimitive(value, handle.adapterContext))
+        }
+
+        override fun <T : Any, Z : Any> has(key: String, dataType: PersistentDataType<T, Z>): Boolean {
+            val value = customDataTags[key] ?: return false
+            return registry.isInstanceOf(dataType, value)
+        }
+
+        override fun <T : Any, Z : Any> get(key: String, dataType: PersistentDataType<T, Z>): Z? {
+            val value = customDataTags[key] ?: return null
+            return dataType.fromPrimitive(registry.extract<T, Tag>(dataType, value), handle.adapterContext)
+        }
+
+        override fun <T : Any, Z : Any> getOrDefault(
+            key: String,
+            dataType: PersistentDataType<T, Z>,
+            defaultValue: Z
+        ): Z {
+            return get(key, dataType) ?: defaultValue
+        }
+
+        override fun remove(key: String) {
+            customDataTags.remove(key)
+        }
+
+        override fun getAllKeys(): MutableSet<String> {
+            return customDataTags.keys
+        }
+
+        override fun getBase(): PersistentDataContainer {
+            return handle
+        }
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/FastItemStackFactory.kt

@@ -0,0 +1,12 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.core.fast.FastItemStack
+import com.willfp.eco.internal.spigot.proxy.FastItemStackFactoryProxy
+import com.willfp.eco.internal.spigot.proxy.common.modern.NewEcoFastItemStack
+import org.bukkit.inventory.ItemStack
+
+class FastItemStackFactory : FastItemStackFactoryProxy {
+    override fun create(itemStack: ItemStack): FastItemStack {
+        return NewEcoFastItemStack(itemStack)
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/MiniMessageTranslator.kt

@@ -0,0 +1,33 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.core.display.Display
+import com.willfp.eco.internal.spigot.proxy.MiniMessageTranslatorProxy
+import com.willfp.eco.util.toLegacy
+import net.kyori.adventure.text.minimessage.MiniMessage
+
+class MiniMessageTranslator : MiniMessageTranslatorProxy {
+    override fun format(message: String): String {
+        var mut = message
+
+        val startsWithPrefix = mut.startsWith(Display.PREFIX)
+        if (startsWithPrefix) {
+            mut = mut.substring(2)
+        }
+
+        mut = mut.replace('§', '&')
+
+        val miniMessage = runCatching {
+            MiniMessage.miniMessage().deserialize(
+                mut
+            ).toLegacy()
+        }.getOrNull() ?: mut
+
+        mut = if (startsWithPrefix) {
+            Display.PREFIX + miniMessage
+        } else {
+            miniMessage
+        }
+
+        return mut
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/PacketHandler.kt

@@ -0,0 +1,46 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.core.EcoPlugin
+import com.willfp.eco.core.packet.PacketListener
+import com.willfp.eco.internal.spigot.proxy.PacketHandlerProxy
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.PacketHeldItemSlot
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.PacketSetSlot
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.PacketWindowItems
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.clearFrames
+import com.willfp.eco.internal.spigot.proxy.v1_21_3.packet.NewItemsPacketOpenWindowMerchant
+import com.willfp.eco.internal.spigot.proxy.v1_21_3.packet.NewItemsPacketSetCreativeSlot
+import net.minecraft.network.protocol.Packet
+import org.bukkit.craftbukkit.entity.CraftPlayer
+import org.bukkit.entity.Player
+
+class PacketHandler : PacketHandlerProxy {
+    override fun sendPacket(player: Player, packet: com.willfp.eco.core.packet.Packet) {
+        if (player !is CraftPlayer) {
+            return
+        }
+
+        val handle = packet.handle
+
+        if (handle !is Packet<*>) {
+            return
+        }
+
+        player.handle.connection.send(handle)
+    }
+
+    override fun clearDisplayFrames() {
+        clearFrames()
+    }
+
+    override fun getPacketListeners(plugin: EcoPlugin): List<PacketListener> {
+        // No PacketAutoRecipe for 1.21.3+ because recipes have been changed internally
+
+        return listOf(
+            PacketHeldItemSlot,
+            NewItemsPacketOpenWindowMerchant,
+            NewItemsPacketSetCreativeSlot,
+            PacketSetSlot,
+            PacketWindowItems(plugin)
+        )
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/SNBTConverter.kt

@@ -0,0 +1,80 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.mojang.serialization.Dynamic
+import com.willfp.eco.core.items.TestableItem
+import com.willfp.eco.core.recipe.parts.EmptyTestableItem
+import com.willfp.eco.internal.spigot.proxy.SNBTConverterProxy
+import net.minecraft.nbt.CompoundTag
+import net.minecraft.nbt.NbtOps
+import net.minecraft.nbt.SnbtPrinterTagVisitor
+import net.minecraft.nbt.TagParser
+import net.minecraft.server.MinecraftServer
+import net.minecraft.util.datafix.fixes.References
+import org.bukkit.Bukkit
+import org.bukkit.craftbukkit.CraftServer
+import org.bukkit.craftbukkit.inventory.CraftItemStack
+import org.bukkit.craftbukkit.util.CraftMagicNumbers
+import org.bukkit.inventory.ItemStack
+
+private val registryAccess = (Bukkit.getServer() as CraftServer).server.registryAccess()
+
+class SNBTConverter : SNBTConverterProxy {
+    private fun parseItemSNBT(snbt: String): CompoundTag? {
+        val nbt = runCatching { TagParser.parseTag(snbt) }.getOrNull() ?: return null
+        val dataVersion = if (nbt.contains("DataVersion")) {
+            nbt.getInt("DataVersion")
+        } else null
+
+        // If the data version is the same as the server's data version, we don't need to fix it
+        if (dataVersion == CraftMagicNumbers.INSTANCE.dataVersion) {
+            return nbt
+        }
+
+        return MinecraftServer.getServer().fixerUpper.update(
+            References.ITEM_STACK,
+            Dynamic(NbtOps.INSTANCE, nbt),
+            dataVersion ?: 3700, // 3700 is the 1.20.4 data version
+            CraftMagicNumbers.INSTANCE.dataVersion
+        ).value as CompoundTag
+    }
+
+    override fun fromSNBT(snbt: String): ItemStack? {
+        val tag = parseItemSNBT(snbt) ?: return null
+        val nms = net.minecraft.world.item.ItemStack.parse(registryAccess, tag).orElse(null) ?: return null
+        return CraftItemStack.asBukkitCopy(nms)
+    }
+
+    override fun toSNBT(itemStack: ItemStack): String {
+        val nms = CraftItemStack.asNMSCopy(itemStack)
+        val tag = nms.save(registryAccess) as CompoundTag
+        tag.putInt("DataVersion", CraftMagicNumbers.INSTANCE.dataVersion)
+        return SnbtPrinterTagVisitor().visit(tag)
+    }
+
+    override fun makeSNBTTestable(snbt: String): TestableItem {
+        val tag = parseItemSNBT(snbt) ?: return EmptyTestableItem()
+        val nms = net.minecraft.world.item.ItemStack.parse(registryAccess, tag).orElse(null)
+            ?: return EmptyTestableItem()
+
+        tag.remove("Count")
+        return SNBTTestableItem(CraftItemStack.asBukkitCopy(nms), tag)
+    }
+
+    class SNBTTestableItem(
+        private val item: ItemStack,
+        private val tag: CompoundTag
+    ) : TestableItem {
+        override fun matches(itemStack: ItemStack?): Boolean {
+            if (itemStack == null) {
+                return false
+            }
+
+            val nms = CraftItemStack.asNMSCopy(itemStack)
+            val nmsTag = nms.save(registryAccess) as CompoundTag
+            nmsTag.remove("Count")
+            return tag.copy().merge(nmsTag) == nmsTag && itemStack.type == item.type
+        }
+
+        override fun getItem(): ItemStack = item
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/Skull.kt

@@ -0,0 +1,18 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.internal.spigot.proxy.SkullProxy
+import com.willfp.eco.internal.spigot.proxy.common.modern.texture
+import org.bukkit.inventory.meta.SkullMeta
+
+class Skull : SkullProxy {
+    override fun setSkullTexture(
+        meta: SkullMeta,
+        base64: String
+    ) {
+        meta.texture = base64
+    }
+
+    override fun getSkullTexture(
+        meta: SkullMeta
+    ): String? = meta.texture
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/TPS.kt

@@ -0,0 +1,11 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3
+
+import com.willfp.eco.internal.spigot.proxy.TPSProxy
+import org.bukkit.Bukkit
+import org.bukkit.craftbukkit.CraftServer
+
+class TPS : TPSProxy {
+    override fun getTPS(): Double {
+        return (Bukkit.getServer() as CraftServer).handle.server.tps1.average
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/entity/EcoEntityController.kt

@@ -0,0 +1,95 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3.entity
+
+import com.willfp.eco.core.entities.ai.CustomGoal
+import com.willfp.eco.core.entities.ai.EntityController
+import com.willfp.eco.core.entities.ai.EntityGoal
+import com.willfp.eco.core.entities.ai.TargetGoal
+import com.willfp.eco.internal.spigot.proxy.common.ai.CustomGoalFactory
+import com.willfp.eco.internal.spigot.proxy.common.ai.getGoalFactory
+import com.willfp.eco.internal.spigot.proxy.common.toPathfinderMob
+import net.minecraft.world.entity.PathfinderMob
+import net.minecraft.world.entity.ai.goal.Goal
+import org.bukkit.entity.Mob
+
+class EcoEntityController<T : Mob>(
+    private val handle: T
+) : EntityController<T> {
+    override fun addEntityGoal(priority: Int, goal: EntityGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        nms.goalSelector.addGoal(
+            priority,
+            goal.getGoalFactory()?.create(goal, nms) ?: return this
+        )
+
+        return this
+    }
+
+    override fun removeEntityGoal(goal: EntityGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        val predicate: (Goal) -> Boolean = if (goal is CustomGoal<*>) {
+            { CustomGoalFactory.isGoalOfType(it, goal) }
+        } else {
+            { goal.getGoalFactory()?.isGoalOfType(it) == true }
+        }
+
+        for (wrapped in nms.goalSelector.availableGoals.toSet()) {
+            if (predicate(wrapped.goal)) {
+                nms.goalSelector.removeGoal(wrapped.goal)
+            }
+        }
+
+        return this
+    }
+
+    override fun clearEntityGoals(): EntityController<T> {
+        val nms = getNms() ?: return this
+        nms.goalSelector.availableGoals.clear()
+        return this
+    }
+
+    override fun addTargetGoal(priority: Int, goal: TargetGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        nms.targetSelector.addGoal(
+            priority, goal.getGoalFactory()?.create(goal, nms) ?: return this
+        )
+
+        nms.targetSelector
+
+        return this
+    }
+
+    override fun removeTargetGoal(goal: TargetGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        val predicate: (Goal) -> Boolean = if (goal is CustomGoal<*>) {
+            { CustomGoalFactory.isGoalOfType(it, goal) }
+        } else {
+            { goal.getGoalFactory()?.isGoalOfType(it) == true }
+        }
+
+        for (wrapped in nms.targetSelector.availableGoals.toSet()) {
+            if (predicate(wrapped.goal)) {
+                nms.targetSelector.removeGoal(wrapped.goal)
+            }
+        }
+
+        return this
+    }
+
+    override fun clearTargetGoals(): EntityController<T> {
+        val nms = getNms() ?: return this
+        nms.targetSelector.availableGoals.clear()
+        return this
+    }
+
+    private fun getNms(): PathfinderMob? {
+        return handle.toPathfinderMob()
+    }
+
+    override fun getEntity(): T {
+        return handle
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/packet/NewItemsPacketOpenWindowMerchant.kt

@@ -0,0 +1,35 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3.packet
+
+import com.willfp.eco.core.display.Display
+import com.willfp.eco.core.packet.PacketEvent
+import com.willfp.eco.core.packet.PacketListener
+import com.willfp.eco.internal.spigot.proxy.common.asBukkitStack
+import net.minecraft.network.protocol.game.ClientboundMerchantOffersPacket
+import net.minecraft.world.item.trading.MerchantOffers
+
+object NewItemsPacketOpenWindowMerchant : PacketListener {
+    private val field = ClientboundMerchantOffersPacket::class.java
+        .declaredFields
+        .first { it.type == MerchantOffers::class.java }
+        .apply { isAccessible = true }
+
+    override fun onSend(event: PacketEvent) {
+        val packet = event.packet.handle as? ClientboundMerchantOffersPacket ?: return
+
+        val offers = MerchantOffers()
+
+        for (offer in packet.offers) {
+            val new = offer.copy()
+
+            Display.display(new.baseCostA.itemStack.asBukkitStack(), event.player)
+            if (new.costB.isPresent) {
+                Display.display(new.costB.get().itemStack.asBukkitStack(), event.player)
+            }
+            Display.display(new.result.asBukkitStack(), event.player)
+
+            offers += new
+        }
+
+        field.set(packet, offers)
+    }
+}

eco-core/core-nms/v1_21_3/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_3/packet/NewItemsPacketSetCreativeSlot.kt

@@ -0,0 +1,19 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_3.packet
+
+import com.willfp.eco.core.display.Display
+import com.willfp.eco.core.packet.PacketEvent
+import com.willfp.eco.core.packet.PacketListener
+import com.willfp.eco.internal.spigot.proxy.common.asBukkitStack
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.DisplayFrame
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.lastDisplayFrame
+import net.minecraft.network.protocol.game.ServerboundSetCreativeModeSlotPacket
+
+object NewItemsPacketSetCreativeSlot : PacketListener {
+    override fun onReceive(event: PacketEvent) {
+        val packet = event.packet.handle as? ServerboundSetCreativeModeSlotPacket ?: return
+
+        Display.revert(packet.itemStack.asBukkitStack())
+
+        event.player.lastDisplayFrame = DisplayFrame.EMPTY
+    }
+}

eco-core/core-nms/v1_21_4/build.gradle.kts

@@ -0,0 +1,52 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
+plugins {
+    id("io.papermc.paperweight.userdev")
+}
+
+group = "com.willfp"
+version = rootProject.version
+
+dependencies {
+    implementation(project(":eco-core:core-nms:modern"))
+    implementation(project(":eco-core:core-nms:common"))
+    paperweight.paperDevBundle("1.21.4-R0.1-SNAPSHOT")
+
+    implementation("net.kyori:adventure-text-minimessage:4.11.0") {
+        version {
+            strictly("4.11.0")
+        }
+        exclude(group = "net.kyori", module = "adventure-api")
+    }
+}
+
+tasks {
+    build {
+        dependsOn(reobfJar)
+    }
+
+    reobfJar {
+        mustRunAfter(shadowJar)
+    }
+
+    shadowJar {
+        relocate(
+            "com.willfp.eco.internal.spigot.proxy.common",
+            "com.willfp.eco.internal.spigot.proxy.v1_21_4.common"
+        )
+        relocate(
+            "net.kyori.adventure.text.minimessage",
+            "com.willfp.eco.internal.spigot.proxy.v1_21_4.minimessage"
+        )
+    }
+
+    compileJava {
+        options.release.set(21)
+    }
+
+    compileKotlin {
+        compilerOptions {
+            jvmTarget.set(JvmTarget.JVM_21)
+        }
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/BukkitCommands.kt

@@ -0,0 +1,35 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.core.command.PluginCommandBase
+import com.willfp.eco.internal.spigot.proxy.BukkitCommandsProxy
+import org.bukkit.Bukkit
+import org.bukkit.command.Command
+import org.bukkit.command.SimpleCommandMap
+import org.bukkit.craftbukkit.CraftServer
+import java.lang.reflect.Field
+
+class BukkitCommands : BukkitCommandsProxy {
+    private val knownCommandsField: Field by lazy {
+        SimpleCommandMap::class.java.getDeclaredField("knownCommands")
+            .apply {
+                isAccessible = true
+            }
+    }
+
+    @Suppress("UNCHECKED_CAST")
+    private val knownCommands: MutableMap<String, Command>
+        get() = knownCommandsField.get(getCommandMap()) as MutableMap<String, Command>
+
+    override fun getCommandMap(): SimpleCommandMap {
+        return (Bukkit.getServer() as CraftServer).commandMap
+    }
+
+    override fun syncCommands() {
+        (Bukkit.getServer() as CraftServer).syncCommands()
+    }
+
+    override fun unregisterCommand(command: PluginCommandBase) {
+        knownCommands.remove(command.name)
+        knownCommands.remove("${command.plugin.name.lowercase()}:${command.name}")
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/CommonsInitializer.kt

@@ -0,0 +1,171 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.core.EcoPlugin
+import com.willfp.eco.internal.spigot.proxy.CommonsInitializerProxy
+import com.willfp.eco.internal.spigot.proxy.common.CommonsProvider
+import com.willfp.eco.internal.spigot.proxy.common.packet.PacketInjectorListener
+import com.willfp.eco.internal.spigot.proxy.common.toResourceLocation
+import net.kyori.adventure.text.Component
+import net.kyori.adventure.text.serializer.json.JSONComponentSerializer
+import net.minecraft.core.component.DataComponents
+import net.minecraft.core.registries.BuiltInRegistries
+import net.minecraft.nbt.CompoundTag
+import net.minecraft.nbt.Tag
+import net.minecraft.resources.ResourceLocation
+import net.minecraft.server.level.ServerPlayer
+import net.minecraft.world.entity.PathfinderMob
+import net.minecraft.world.item.Item
+import org.bukkit.Bukkit
+import org.bukkit.Material
+import org.bukkit.NamespacedKey
+import org.bukkit.craftbukkit.CraftServer
+import org.bukkit.craftbukkit.entity.CraftEntity
+import org.bukkit.craftbukkit.entity.CraftMob
+import org.bukkit.craftbukkit.entity.CraftPlayer
+import org.bukkit.craftbukkit.inventory.CraftItemStack
+import org.bukkit.craftbukkit.inventory.CraftMetaArmor
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataContainer
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataTypeRegistry
+import org.bukkit.craftbukkit.util.CraftMagicNumbers
+import org.bukkit.craftbukkit.util.CraftNamespacedKey
+import org.bukkit.entity.LivingEntity
+import org.bukkit.entity.Mob
+import org.bukkit.entity.Player
+import org.bukkit.inventory.ItemStack
+import org.bukkit.persistence.PersistentDataContainer
+import java.lang.reflect.Field
+
+class CommonsInitializer : CommonsInitializerProxy {
+    override fun init(plugin: EcoPlugin) {
+        CommonsProvider.setIfNeeded(CommonsProviderImpl)
+        plugin.onEnable {
+            plugin.eventManager.registerListener(PacketInjectorListener)
+        }
+    }
+
+    object CommonsProviderImpl : CommonsProvider {
+        private val cisHandle: Field = CraftItemStack::class.java.getDeclaredField("handle").apply {
+            isAccessible = true
+        }
+
+        private val pdcRegsitry = CraftMetaArmor::class.java
+            .superclass // Access CraftMetaItem
+            .getDeclaredField("DATA_TYPE_REGISTRY")
+            .apply { isAccessible = true }
+            .get(null) as CraftPersistentDataTypeRegistry
+
+        override val nbtTagString = CraftMagicNumbers.NBT.TAG_STRING
+
+        override fun toPathfinderMob(mob: Mob): PathfinderMob? {
+            val craft = mob as? CraftMob ?: return null
+            return craft.handle as? PathfinderMob
+        }
+
+        override fun toResourceLocation(namespacedKey: NamespacedKey): ResourceLocation =
+            CraftNamespacedKey.toMinecraft(namespacedKey)
+
+        override fun asNMSStack(itemStack: ItemStack): net.minecraft.world.item.ItemStack {
+            return if (itemStack !is CraftItemStack) {
+                CraftItemStack.asNMSCopy(itemStack)
+            } else {
+                cisHandle[itemStack] as net.minecraft.world.item.ItemStack? ?: CraftItemStack.asNMSCopy(itemStack)
+            }
+        }
+
+        override fun asBukkitStack(itemStack: net.minecraft.world.item.ItemStack): ItemStack {
+            return CraftItemStack.asCraftMirror(itemStack)
+        }
+
+        override fun mergeIfNeeded(itemStack: ItemStack, nmsStack: net.minecraft.world.item.ItemStack) {
+            if (itemStack !is CraftItemStack) {
+                itemStack.itemMeta = CraftItemStack.asCraftMirror(nmsStack).itemMeta
+            }
+        }
+
+        override fun toBukkitEntity(entity: net.minecraft.world.entity.LivingEntity): LivingEntity? =
+            CraftEntity.getEntity(Bukkit.getServer() as CraftServer, entity) as? LivingEntity
+
+        override fun makePdc(tag: CompoundTag, base: Boolean): PersistentDataContainer {
+            fun emptyPdc(): CraftPersistentDataContainer = CraftPersistentDataContainer(pdcRegsitry)
+
+            fun CompoundTag?.toPdc(): PersistentDataContainer {
+                val pdc = emptyPdc()
+                this ?: return pdc
+                val keys = this.allKeys
+                for (key in keys) {
+                    pdc.put(key, this[key])
+                }
+
+                return pdc
+            }
+
+            return if (base) {
+                tag.toPdc()
+            } else {
+                if (tag.contains("PublicBukkitValues")) {
+                    tag.getCompound("PublicBukkitValues").toPdc()
+                } else {
+                    emptyPdc()
+                }
+            }
+        }
+
+        override fun setPdc(
+            tag: CompoundTag,
+            pdc: PersistentDataContainer?,
+            item: net.minecraft.world.item.ItemStack?
+        ) {
+            fun CraftPersistentDataContainer.toTag(): CompoundTag {
+                val compound = CompoundTag()
+                val rawPublicMap: Map<String, Tag> = this.raw
+                for ((key, value) in rawPublicMap) {
+                    compound.put(key, value)
+                }
+
+                return compound
+            }
+
+            val container = when (pdc) {
+                is CraftPersistentDataContainer? -> pdc
+                else -> null
+            }
+
+            if (item != null) {
+                if (container != null && !container.isEmpty) {
+                    for (key in tag.allKeys.toSet()) {
+                        tag.remove(key)
+                    }
+
+                    tag.merge(container.toTag())
+                } else {
+                    item.remove(DataComponents.CUSTOM_DATA)
+                }
+            } else {
+                if (container != null && !container.isEmpty) {
+                    tag.put("PublicBukkitValues", container.toTag())
+                } else {
+                    tag.remove("PublicBukkitValues")
+                }
+            }
+        }
+
+        override fun materialToItem(material: Material): Item =
+            BuiltInRegistries.ITEM.getOptional(material.key.toResourceLocation())
+                .orElseThrow { IllegalArgumentException("Material is not item!") }
+
+        override fun itemToMaterial(item: Item) =
+            Material.getMaterial(BuiltInRegistries.ITEM.getKey(item).path.uppercase())
+                ?: throw IllegalArgumentException("Invalid material!")
+
+        override fun toNMS(player: Player): ServerPlayer {
+            return (player as CraftPlayer).handle
+        }
+
+        override fun toNMS(component: Component): net.minecraft.network.chat.Component {
+            val json = JSONComponentSerializer.json().serialize(component)
+            val holderLookupProvider = (Bukkit.getServer() as CraftServer).server.registryAccess()
+
+            return net.minecraft.network.chat.Component.Serializer.fromJson(json, holderLookupProvider)!!
+        }
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/DisplayName.kt

@@ -0,0 +1,57 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.core.packet.Packet
+import com.willfp.eco.core.packet.sendPacket
+import com.willfp.eco.internal.spigot.proxy.DisplayNameProxy
+import com.willfp.eco.internal.spigot.proxy.common.toNMS
+import net.kyori.adventure.text.Component
+import net.minecraft.network.protocol.game.ClientboundSetEntityDataPacket
+import net.minecraft.network.syncher.EntityDataAccessor
+import net.minecraft.network.syncher.SynchedEntityData
+import net.minecraft.world.entity.Entity
+import org.bukkit.craftbukkit.entity.CraftLivingEntity
+import org.bukkit.entity.LivingEntity
+import org.bukkit.entity.Player
+import java.util.Optional
+
+@Suppress("UNCHECKED_CAST")
+class DisplayName : DisplayNameProxy {
+    private val displayNameAccessor = Entity::class.java
+        .declaredFields
+        .filter { it.type == EntityDataAccessor::class.java }
+        .toList()[2]
+        .apply { isAccessible = true }
+        .get(null) as EntityDataAccessor<Optional<net.minecraft.network.chat.Component>>
+
+    private val customNameVisibleAccessor = Entity::class.java
+        .declaredFields
+        .filter { it.type == EntityDataAccessor::class.java }
+        .toList()[3]
+        .apply { isAccessible = true }
+        .get(null) as EntityDataAccessor<Boolean>
+
+    override fun setClientsideDisplayName(
+        entity: LivingEntity,
+        player: Player,
+        displayName: Component,
+        visible: Boolean
+    ) {
+        if (entity !is CraftLivingEntity) {
+            return
+        }
+
+        val nmsComponent = displayName.toNMS()
+
+        val nmsEntity = entity.handle
+
+        val packet = ClientboundSetEntityDataPacket(
+            nmsEntity.id,
+            listOf(
+                SynchedEntityData.DataValue.create(displayNameAccessor, Optional.of(nmsComponent)),
+                SynchedEntityData.DataValue.create(customNameVisibleAccessor, visible)
+            )
+        )
+
+        player.sendPacket(Packet(packet))
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/DummyEntityFactory.kt

@@ -0,0 +1,15 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.internal.entities.EcoDummyEntity
+import com.willfp.eco.internal.spigot.proxy.DummyEntityFactoryProxy
+import org.bukkit.Location
+import org.bukkit.craftbukkit.CraftWorld
+import org.bukkit.entity.Entity
+import org.bukkit.entity.Zombie
+
+class DummyEntityFactory : DummyEntityFactoryProxy {
+    override fun createDummyEntity(location: Location): Entity {
+        val world = location.world as CraftWorld
+        return EcoDummyEntity(world.createEntity(location, Zombie::class.java))
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/EntityControllerFactory.kt

@@ -0,0 +1,12 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.core.entities.ai.EntityController
+import com.willfp.eco.internal.spigot.proxy.EntityControllerFactoryProxy
+import com.willfp.eco.internal.spigot.proxy.v1_21_4.entity.EcoEntityController
+import org.bukkit.entity.Mob
+
+class EntityControllerFactory : EntityControllerFactoryProxy {
+    override fun <T : Mob> createEntityController(entity: T): EntityController<T> {
+        return EcoEntityController(entity)
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/ExtendedPersistentDataContainerFactory.kt

@@ -0,0 +1,91 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.core.data.ExtendedPersistentDataContainer
+import com.willfp.eco.internal.spigot.proxy.ExtendedPersistentDataContainerFactoryProxy
+import net.minecraft.nbt.Tag
+import org.bukkit.Material
+import org.bukkit.craftbukkit.inventory.CraftItemStack
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataContainer
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataTypeRegistry
+import org.bukkit.inventory.ItemStack
+import org.bukkit.persistence.PersistentDataContainer
+import org.bukkit.persistence.PersistentDataType
+import java.lang.reflect.Field
+
+class ExtendedPersistentDataContainerFactory : ExtendedPersistentDataContainerFactoryProxy {
+    private val registry: CraftPersistentDataTypeRegistry
+
+    init {
+        /*
+         Can't grab actual instance since it's in CraftMetaItem (which is package-private)
+         And getting it would mean more janky reflection
+         */
+        val item = CraftItemStack.asCraftCopy(ItemStack(Material.STONE))
+        val pdc = item.itemMeta!!.persistentDataContainer
+
+        // Cross-version compatibility:
+        val registryField: Field = try {
+            CraftPersistentDataContainer::class.java.getDeclaredField("registry")
+        } catch (e: NoSuchFieldException) {
+            CraftPersistentDataContainer::class.java.superclass.getDeclaredField("registry")
+        }
+
+        this.registry = registryField
+            .apply { isAccessible = true }.get(pdc) as CraftPersistentDataTypeRegistry
+    }
+
+    override fun adapt(pdc: PersistentDataContainer): ExtendedPersistentDataContainer {
+        return when (pdc) {
+            is CraftPersistentDataContainer -> EcoPersistentDataContainer(pdc)
+            else -> throw IllegalArgumentException("Custom PDC instance ${pdc::class.java.name} is not supported!")
+        }
+    }
+
+    override fun newPdc(): PersistentDataContainer {
+        return CraftPersistentDataContainer(registry)
+    }
+
+    inner class EcoPersistentDataContainer(
+        private val handle: CraftPersistentDataContainer
+    ) : ExtendedPersistentDataContainer {
+        @Suppress("UNCHECKED_CAST")
+        private val customDataTags: MutableMap<String, Tag> =
+            CraftPersistentDataContainer::class.java.getDeclaredField("customDataTags")
+                .apply { isAccessible = true }.get(handle) as MutableMap<String, Tag>
+
+        override fun <T : Any, Z : Any> set(key: String, dataType: PersistentDataType<T, Z>, value: Z) {
+            customDataTags[key] =
+                registry.wrap(dataType, dataType.toPrimitive(value, handle.adapterContext))
+        }
+
+        override fun <T : Any, Z : Any> has(key: String, dataType: PersistentDataType<T, Z>): Boolean {
+            val value = customDataTags[key] ?: return false
+            return registry.isInstanceOf(dataType, value)
+        }
+
+        override fun <T : Any, Z : Any> get(key: String, dataType: PersistentDataType<T, Z>): Z? {
+            val value = customDataTags[key] ?: return null
+            return dataType.fromPrimitive(registry.extract<T, Tag>(dataType, value), handle.adapterContext)
+        }
+
+        override fun <T : Any, Z : Any> getOrDefault(
+            key: String,
+            dataType: PersistentDataType<T, Z>,
+            defaultValue: Z
+        ): Z {
+            return get(key, dataType) ?: defaultValue
+        }
+
+        override fun remove(key: String) {
+            customDataTags.remove(key)
+        }
+
+        override fun getAllKeys(): MutableSet<String> {
+            return customDataTags.keys
+        }
+
+        override fun getBase(): PersistentDataContainer {
+            return handle
+        }
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/FastItemStackFactory.kt

@@ -0,0 +1,12 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.core.fast.FastItemStack
+import com.willfp.eco.internal.spigot.proxy.FastItemStackFactoryProxy
+import com.willfp.eco.internal.spigot.proxy.common.modern.NewEcoFastItemStack
+import org.bukkit.inventory.ItemStack
+
+class FastItemStackFactory : FastItemStackFactoryProxy {
+    override fun create(itemStack: ItemStack): FastItemStack {
+        return NewEcoFastItemStack(itemStack)
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/MiniMessageTranslator.kt

@@ -0,0 +1,33 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.core.display.Display
+import com.willfp.eco.internal.spigot.proxy.MiniMessageTranslatorProxy
+import com.willfp.eco.util.toLegacy
+import net.kyori.adventure.text.minimessage.MiniMessage
+
+class MiniMessageTranslator : MiniMessageTranslatorProxy {
+    override fun format(message: String): String {
+        var mut = message
+
+        val startsWithPrefix = mut.startsWith(Display.PREFIX)
+        if (startsWithPrefix) {
+            mut = mut.substring(2)
+        }
+
+        mut = mut.replace('§', '&')
+
+        val miniMessage = runCatching {
+            MiniMessage.miniMessage().deserialize(
+                mut
+            ).toLegacy()
+        }.getOrNull() ?: mut
+
+        mut = if (startsWithPrefix) {
+            Display.PREFIX + miniMessage
+        } else {
+            miniMessage
+        }
+
+        return mut
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/PacketHandler.kt

@@ -0,0 +1,46 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.core.EcoPlugin
+import com.willfp.eco.core.packet.PacketListener
+import com.willfp.eco.internal.spigot.proxy.PacketHandlerProxy
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.PacketHeldItemSlot
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.PacketSetSlot
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.PacketWindowItems
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.clearFrames
+import com.willfp.eco.internal.spigot.proxy.v1_21_4.packet.NewItemsPacketOpenWindowMerchant
+import com.willfp.eco.internal.spigot.proxy.v1_21_4.packet.NewItemsPacketSetCreativeSlot
+import net.minecraft.network.protocol.Packet
+import org.bukkit.craftbukkit.entity.CraftPlayer
+import org.bukkit.entity.Player
+
+class PacketHandler : PacketHandlerProxy {
+    override fun sendPacket(player: Player, packet: com.willfp.eco.core.packet.Packet) {
+        if (player !is CraftPlayer) {
+            return
+        }
+
+        val handle = packet.handle
+
+        if (handle !is Packet<*>) {
+            return
+        }
+
+        player.handle.connection.send(handle)
+    }
+
+    override fun clearDisplayFrames() {
+        clearFrames()
+    }
+
+    override fun getPacketListeners(plugin: EcoPlugin): List<PacketListener> {
+        // No PacketAutoRecipe for 1.21.3+ because recipes have been changed internally
+
+        return listOf(
+            PacketHeldItemSlot,
+            NewItemsPacketOpenWindowMerchant,
+            NewItemsPacketSetCreativeSlot,
+            PacketSetSlot,
+            PacketWindowItems(plugin)
+        )
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/SNBTConverter.kt

@@ -0,0 +1,80 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.mojang.serialization.Dynamic
+import com.willfp.eco.core.items.TestableItem
+import com.willfp.eco.core.recipe.parts.EmptyTestableItem
+import com.willfp.eco.internal.spigot.proxy.SNBTConverterProxy
+import net.minecraft.nbt.CompoundTag
+import net.minecraft.nbt.NbtOps
+import net.minecraft.nbt.SnbtPrinterTagVisitor
+import net.minecraft.nbt.TagParser
+import net.minecraft.server.MinecraftServer
+import net.minecraft.util.datafix.fixes.References
+import org.bukkit.Bukkit
+import org.bukkit.craftbukkit.CraftServer
+import org.bukkit.craftbukkit.inventory.CraftItemStack
+import org.bukkit.craftbukkit.util.CraftMagicNumbers
+import org.bukkit.inventory.ItemStack
+
+private val registryAccess = (Bukkit.getServer() as CraftServer).server.registryAccess()
+
+class SNBTConverter : SNBTConverterProxy {
+    private fun parseItemSNBT(snbt: String): CompoundTag? {
+        val nbt = runCatching { TagParser.parseTag(snbt) }.getOrNull() ?: return null
+        val dataVersion = if (nbt.contains("DataVersion")) {
+            nbt.getInt("DataVersion")
+        } else null
+
+        // If the data version is the same as the server's data version, we don't need to fix it
+        if (dataVersion == CraftMagicNumbers.INSTANCE.dataVersion) {
+            return nbt
+        }
+
+        return MinecraftServer.getServer().fixerUpper.update(
+            References.ITEM_STACK,
+            Dynamic(NbtOps.INSTANCE, nbt),
+            dataVersion ?: 3700, // 3700 is the 1.20.4 data version
+            CraftMagicNumbers.INSTANCE.dataVersion
+        ).value as CompoundTag
+    }
+
+    override fun fromSNBT(snbt: String): ItemStack? {
+        val tag = parseItemSNBT(snbt) ?: return null
+        val nms = net.minecraft.world.item.ItemStack.parse(registryAccess, tag).orElse(null) ?: return null
+        return CraftItemStack.asBukkitCopy(nms)
+    }
+
+    override fun toSNBT(itemStack: ItemStack): String {
+        val nms = CraftItemStack.asNMSCopy(itemStack)
+        val tag = nms.save(registryAccess) as CompoundTag
+        tag.putInt("DataVersion", CraftMagicNumbers.INSTANCE.dataVersion)
+        return SnbtPrinterTagVisitor().visit(tag)
+    }
+
+    override fun makeSNBTTestable(snbt: String): TestableItem {
+        val tag = parseItemSNBT(snbt) ?: return EmptyTestableItem()
+        val nms = net.minecraft.world.item.ItemStack.parse(registryAccess, tag).orElse(null)
+            ?: return EmptyTestableItem()
+
+        tag.remove("Count")
+        return SNBTTestableItem(CraftItemStack.asBukkitCopy(nms), tag)
+    }
+
+    class SNBTTestableItem(
+        private val item: ItemStack,
+        private val tag: CompoundTag
+    ) : TestableItem {
+        override fun matches(itemStack: ItemStack?): Boolean {
+            if (itemStack == null) {
+                return false
+            }
+
+            val nms = CraftItemStack.asNMSCopy(itemStack)
+            val nmsTag = nms.save(registryAccess) as CompoundTag
+            nmsTag.remove("Count")
+            return tag.copy().merge(nmsTag) == nmsTag && itemStack.type == item.type
+        }
+
+        override fun getItem(): ItemStack = item
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/Skull.kt

@@ -0,0 +1,18 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.internal.spigot.proxy.SkullProxy
+import com.willfp.eco.internal.spigot.proxy.common.modern.texture
+import org.bukkit.inventory.meta.SkullMeta
+
+class Skull : SkullProxy {
+    override fun setSkullTexture(
+        meta: SkullMeta,
+        base64: String
+    ) {
+        meta.texture = base64
+    }
+
+    override fun getSkullTexture(
+        meta: SkullMeta
+    ): String? = meta.texture
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/TPS.kt

@@ -0,0 +1,11 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4
+
+import com.willfp.eco.internal.spigot.proxy.TPSProxy
+import org.bukkit.Bukkit
+import org.bukkit.craftbukkit.CraftServer
+
+class TPS : TPSProxy {
+    override fun getTPS(): Double {
+        return (Bukkit.getServer() as CraftServer).handle.server.tps1.average
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/entity/EcoEntityController.kt

@@ -0,0 +1,95 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4.entity
+
+import com.willfp.eco.core.entities.ai.CustomGoal
+import com.willfp.eco.core.entities.ai.EntityController
+import com.willfp.eco.core.entities.ai.EntityGoal
+import com.willfp.eco.core.entities.ai.TargetGoal
+import com.willfp.eco.internal.spigot.proxy.common.ai.CustomGoalFactory
+import com.willfp.eco.internal.spigot.proxy.common.ai.getGoalFactory
+import com.willfp.eco.internal.spigot.proxy.common.toPathfinderMob
+import net.minecraft.world.entity.PathfinderMob
+import net.minecraft.world.entity.ai.goal.Goal
+import org.bukkit.entity.Mob
+
+class EcoEntityController<T : Mob>(
+    private val handle: T
+) : EntityController<T> {
+    override fun addEntityGoal(priority: Int, goal: EntityGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        nms.goalSelector.addGoal(
+            priority,
+            goal.getGoalFactory()?.create(goal, nms) ?: return this
+        )
+
+        return this
+    }
+
+    override fun removeEntityGoal(goal: EntityGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        val predicate: (Goal) -> Boolean = if (goal is CustomGoal<*>) {
+            { CustomGoalFactory.isGoalOfType(it, goal) }
+        } else {
+            { goal.getGoalFactory()?.isGoalOfType(it) == true }
+        }
+
+        for (wrapped in nms.goalSelector.availableGoals.toSet()) {
+            if (predicate(wrapped.goal)) {
+                nms.goalSelector.removeGoal(wrapped.goal)
+            }
+        }
+
+        return this
+    }
+
+    override fun clearEntityGoals(): EntityController<T> {
+        val nms = getNms() ?: return this
+        nms.goalSelector.availableGoals.clear()
+        return this
+    }
+
+    override fun addTargetGoal(priority: Int, goal: TargetGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        nms.targetSelector.addGoal(
+            priority, goal.getGoalFactory()?.create(goal, nms) ?: return this
+        )
+
+        nms.targetSelector
+
+        return this
+    }
+
+    override fun removeTargetGoal(goal: TargetGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        val predicate: (Goal) -> Boolean = if (goal is CustomGoal<*>) {
+            { CustomGoalFactory.isGoalOfType(it, goal) }
+        } else {
+            { goal.getGoalFactory()?.isGoalOfType(it) == true }
+        }
+
+        for (wrapped in nms.targetSelector.availableGoals.toSet()) {
+            if (predicate(wrapped.goal)) {
+                nms.targetSelector.removeGoal(wrapped.goal)
+            }
+        }
+
+        return this
+    }
+
+    override fun clearTargetGoals(): EntityController<T> {
+        val nms = getNms() ?: return this
+        nms.targetSelector.availableGoals.clear()
+        return this
+    }
+
+    private fun getNms(): PathfinderMob? {
+        return handle.toPathfinderMob()
+    }
+
+    override fun getEntity(): T {
+        return handle
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/packet/NewItemsPacketOpenWindowMerchant.kt

@@ -0,0 +1,35 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4.packet
+
+import com.willfp.eco.core.display.Display
+import com.willfp.eco.core.packet.PacketEvent
+import com.willfp.eco.core.packet.PacketListener
+import com.willfp.eco.internal.spigot.proxy.common.asBukkitStack
+import net.minecraft.network.protocol.game.ClientboundMerchantOffersPacket
+import net.minecraft.world.item.trading.MerchantOffers
+
+object NewItemsPacketOpenWindowMerchant : PacketListener {
+    private val field = ClientboundMerchantOffersPacket::class.java
+        .declaredFields
+        .first { it.type == MerchantOffers::class.java }
+        .apply { isAccessible = true }
+
+    override fun onSend(event: PacketEvent) {
+        val packet = event.packet.handle as? ClientboundMerchantOffersPacket ?: return
+
+        val offers = MerchantOffers()
+
+        for (offer in packet.offers) {
+            val new = offer.copy()
+
+            Display.display(new.baseCostA.itemStack.asBukkitStack(), event.player)
+            if (new.costB.isPresent) {
+                Display.display(new.costB.get().itemStack.asBukkitStack(), event.player)
+            }
+            Display.display(new.result.asBukkitStack(), event.player)
+
+            offers += new
+        }
+
+        field.set(packet, offers)
+    }
+}

eco-core/core-nms/v1_21_4/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_4/packet/NewItemsPacketSetCreativeSlot.kt

@@ -0,0 +1,20 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_4.packet
+
+import com.willfp.eco.core.display.Display
+import com.willfp.eco.core.packet.PacketEvent
+import com.willfp.eco.core.packet.PacketListener
+import com.willfp.eco.internal.spigot.proxy.common.asBukkitStack
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.DisplayFrame
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.lastDisplayFrame
+import net.minecraft.network.protocol.game.ClientboundContainerSetContentPacket
+import net.minecraft.network.protocol.game.ServerboundSetCreativeModeSlotPacket
+
+object NewItemsPacketSetCreativeSlot : PacketListener {
+    override fun onReceive(event: PacketEvent) {
+        val packet = event.packet.handle as? ServerboundSetCreativeModeSlotPacket ?: return
+
+        Display.revert(packet.itemStack.asBukkitStack())
+
+        event.player.lastDisplayFrame = DisplayFrame.EMPTY
+    }
+}

eco-core/core-nms/v1_21_5/build.gradle.kts

@@ -0,0 +1,52 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
+plugins {
+    id("io.papermc.paperweight.userdev")
+}
+
+group = "com.willfp"
+version = rootProject.version
+
+dependencies {
+    implementation(project(":eco-core:core-nms:modern"))
+    implementation(project(":eco-core:core-nms:common"))
+    paperweight.paperDevBundle("1.21.5-R0.1-SNAPSHOT")
+
+    implementation("net.kyori:adventure-text-minimessage:4.11.0") {
+        version {
+            strictly("4.11.0")
+        }
+        exclude(group = "net.kyori", module = "adventure-api")
+    }
+}
+
+tasks {
+    build {
+        dependsOn(reobfJar)
+    }
+
+    reobfJar {
+        mustRunAfter(shadowJar)
+    }
+
+    shadowJar {
+        relocate(
+            "com.willfp.eco.internal.spigot.proxy.common",
+            "com.willfp.eco.internal.spigot.proxy.v1_21_5.common"
+        )
+        relocate(
+            "net.kyori.adventure.text.minimessage",
+            "com.willfp.eco.internal.spigot.proxy.v1_21_5.minimessage"
+        )
+    }
+
+    compileJava {
+        options.release.set(21)
+    }
+
+    compileKotlin {
+        compilerOptions {
+            jvmTarget.set(JvmTarget.JVM_21)
+        }
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/BukkitCommands.kt

@@ -0,0 +1,35 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.core.command.PluginCommandBase
+import com.willfp.eco.internal.spigot.proxy.BukkitCommandsProxy
+import org.bukkit.Bukkit
+import org.bukkit.command.Command
+import org.bukkit.command.SimpleCommandMap
+import org.bukkit.craftbukkit.CraftServer
+import java.lang.reflect.Field
+
+class BukkitCommands : BukkitCommandsProxy {
+    private val knownCommandsField: Field by lazy {
+        SimpleCommandMap::class.java.getDeclaredField("knownCommands")
+            .apply {
+                isAccessible = true
+            }
+    }
+
+    @Suppress("UNCHECKED_CAST")
+    private val knownCommands: MutableMap<String, Command>
+        get() = knownCommandsField.get(getCommandMap()) as MutableMap<String, Command>
+
+    override fun getCommandMap(): SimpleCommandMap {
+        return (Bukkit.getServer() as CraftServer).commandMap
+    }
+
+    override fun syncCommands() {
+        (Bukkit.getServer() as CraftServer).syncCommands()
+    }
+
+    override fun unregisterCommand(command: PluginCommandBase) {
+        knownCommands.remove(command.name)
+        knownCommands.remove("${command.plugin.name.lowercase()}:${command.name}")
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/CommonsInitializer.kt

@@ -0,0 +1,171 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.core.EcoPlugin
+import com.willfp.eco.internal.spigot.proxy.CommonsInitializerProxy
+import com.willfp.eco.internal.spigot.proxy.common.CommonsProvider
+import com.willfp.eco.internal.spigot.proxy.common.packet.PacketInjectorListener
+import com.willfp.eco.internal.spigot.proxy.common.toResourceLocation
+import net.kyori.adventure.text.Component
+import net.kyori.adventure.text.serializer.json.JSONComponentSerializer
+import net.minecraft.core.component.DataComponents
+import net.minecraft.core.registries.BuiltInRegistries
+import net.minecraft.nbt.CompoundTag
+import net.minecraft.nbt.Tag
+import net.minecraft.resources.ResourceLocation
+import net.minecraft.server.level.ServerPlayer
+import net.minecraft.world.entity.PathfinderMob
+import net.minecraft.world.item.Item
+import org.bukkit.Bukkit
+import org.bukkit.Material
+import org.bukkit.NamespacedKey
+import org.bukkit.craftbukkit.CraftServer
+import org.bukkit.craftbukkit.entity.CraftEntity
+import org.bukkit.craftbukkit.entity.CraftMob
+import org.bukkit.craftbukkit.entity.CraftPlayer
+import org.bukkit.craftbukkit.inventory.CraftItemStack
+import org.bukkit.craftbukkit.inventory.CraftMetaArmor
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataContainer
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataTypeRegistry
+import org.bukkit.craftbukkit.util.CraftMagicNumbers
+import org.bukkit.craftbukkit.util.CraftNamespacedKey
+import org.bukkit.entity.LivingEntity
+import org.bukkit.entity.Mob
+import org.bukkit.entity.Player
+import org.bukkit.inventory.ItemStack
+import org.bukkit.persistence.PersistentDataContainer
+import java.lang.reflect.Field
+
+class CommonsInitializer : CommonsInitializerProxy {
+    override fun init(plugin: EcoPlugin) {
+        CommonsProvider.setIfNeeded(CommonsProviderImpl)
+        plugin.onEnable {
+            plugin.eventManager.registerListener(PacketInjectorListener)
+        }
+    }
+
+    object CommonsProviderImpl : CommonsProvider {
+        private val cisHandle: Field = CraftItemStack::class.java.getDeclaredField("handle").apply {
+            isAccessible = true
+        }
+
+        private val pdcRegsitry = CraftMetaArmor::class.java
+            .superclass // Access CraftMetaItem
+            .getDeclaredField("DATA_TYPE_REGISTRY")
+            .apply { isAccessible = true }
+            .get(null) as CraftPersistentDataTypeRegistry
+
+        override val nbtTagString = 8
+
+        override fun toPathfinderMob(mob: Mob): PathfinderMob? {
+            val craft = mob as? CraftMob ?: return null
+            return craft.handle as? PathfinderMob
+        }
+
+        override fun toResourceLocation(namespacedKey: NamespacedKey): ResourceLocation =
+            CraftNamespacedKey.toMinecraft(namespacedKey)
+
+        override fun asNMSStack(itemStack: ItemStack): net.minecraft.world.item.ItemStack {
+            return if (itemStack !is CraftItemStack) {
+                CraftItemStack.asNMSCopy(itemStack)
+            } else {
+                cisHandle[itemStack] as net.minecraft.world.item.ItemStack? ?: CraftItemStack.asNMSCopy(itemStack)
+            }
+        }
+
+        override fun asBukkitStack(itemStack: net.minecraft.world.item.ItemStack): ItemStack {
+            return CraftItemStack.asCraftMirror(itemStack)
+        }
+
+        override fun mergeIfNeeded(itemStack: ItemStack, nmsStack: net.minecraft.world.item.ItemStack) {
+            if (itemStack !is CraftItemStack) {
+                itemStack.itemMeta = CraftItemStack.asCraftMirror(nmsStack).itemMeta
+            }
+        }
+
+        override fun toBukkitEntity(entity: net.minecraft.world.entity.LivingEntity): LivingEntity? =
+            CraftEntity.getEntity(Bukkit.getServer() as CraftServer, entity) as? LivingEntity
+
+        override fun makePdc(tag: CompoundTag, base: Boolean): PersistentDataContainer {
+            fun emptyPdc(): CraftPersistentDataContainer = CraftPersistentDataContainer(pdcRegsitry)
+
+            fun CompoundTag?.toPdc(): PersistentDataContainer {
+                val pdc = emptyPdc()
+                this ?: return pdc
+                val keys = this.keySet()
+                for (key in keys) {
+                    pdc.put(key, this[key])
+                }
+
+                return pdc
+            }
+
+            return if (base) {
+                tag.toPdc()
+            } else {
+                if (tag.contains("PublicBukkitValues")) {
+                    tag.getCompound("PublicBukkitValues").get().toPdc()
+                } else {
+                    emptyPdc()
+                }
+            }
+        }
+
+        override fun setPdc(
+            tag: CompoundTag,
+            pdc: PersistentDataContainer?,
+            item: net.minecraft.world.item.ItemStack?
+        ) {
+            fun CraftPersistentDataContainer.toTag(): CompoundTag {
+                val compound = CompoundTag()
+                val rawPublicMap: Map<String, Tag> = this.raw
+                for ((key, value) in rawPublicMap) {
+                    compound.put(key, value)
+                }
+
+                return compound
+            }
+
+            val container = when (pdc) {
+                is CraftPersistentDataContainer? -> pdc
+                else -> null
+            }
+
+            if (item != null) {
+                if (container != null && !container.isEmpty) {
+                    for (key in tag.keySet()) {
+                        tag.remove(key)
+                    }
+
+                    tag.merge(container.toTag())
+                } else {
+                    item.remove(DataComponents.CUSTOM_DATA)
+                }
+            } else {
+                if (container != null && !container.isEmpty) {
+                    tag.put("PublicBukkitValues", container.toTag())
+                } else {
+                    tag.remove("PublicBukkitValues")
+                }
+            }
+        }
+
+        override fun materialToItem(material: Material): Item =
+            BuiltInRegistries.ITEM.getOptional(material.key.toResourceLocation())
+                .orElseThrow { IllegalArgumentException("Material is not item!") }
+
+        override fun itemToMaterial(item: Item) =
+            Material.getMaterial(BuiltInRegistries.ITEM.getKey(item).path.uppercase())
+                ?: throw IllegalArgumentException("Invalid material!")
+
+        override fun toNMS(player: Player): ServerPlayer {
+            return (player as CraftPlayer).handle
+        }
+
+        override fun toNMS(component: Component): net.minecraft.network.chat.Component {
+            val json = JSONComponentSerializer.json().serialize(component)
+            val holderLookupProvider = (Bukkit.getServer() as CraftServer).server.registryAccess()
+
+            return net.minecraft.network.chat.Component.Serializer.fromJson(json, holderLookupProvider)!!
+        }
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/DisplayName.kt

@@ -0,0 +1,57 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.core.packet.Packet
+import com.willfp.eco.core.packet.sendPacket
+import com.willfp.eco.internal.spigot.proxy.DisplayNameProxy
+import com.willfp.eco.internal.spigot.proxy.common.toNMS
+import net.kyori.adventure.text.Component
+import net.minecraft.network.protocol.game.ClientboundSetEntityDataPacket
+import net.minecraft.network.syncher.EntityDataAccessor
+import net.minecraft.network.syncher.SynchedEntityData
+import net.minecraft.world.entity.Entity
+import org.bukkit.craftbukkit.entity.CraftLivingEntity
+import org.bukkit.entity.LivingEntity
+import org.bukkit.entity.Player
+import java.util.Optional
+
+@Suppress("UNCHECKED_CAST")
+class DisplayName : DisplayNameProxy {
+    private val displayNameAccessor = Entity::class.java
+        .declaredFields
+        .filter { it.type == EntityDataAccessor::class.java }
+        .toList()[2]
+        .apply { isAccessible = true }
+        .get(null) as EntityDataAccessor<Optional<net.minecraft.network.chat.Component>>
+
+    private val customNameVisibleAccessor = Entity::class.java
+        .declaredFields
+        .filter { it.type == EntityDataAccessor::class.java }
+        .toList()[3]
+        .apply { isAccessible = true }
+        .get(null) as EntityDataAccessor<Boolean>
+
+    override fun setClientsideDisplayName(
+        entity: LivingEntity,
+        player: Player,
+        displayName: Component,
+        visible: Boolean
+    ) {
+        if (entity !is CraftLivingEntity) {
+            return
+        }
+
+        val nmsComponent = displayName.toNMS()
+
+        val nmsEntity = entity.handle
+
+        val packet = ClientboundSetEntityDataPacket(
+            nmsEntity.id,
+            listOf(
+                SynchedEntityData.DataValue.create(displayNameAccessor, Optional.of(nmsComponent)),
+                SynchedEntityData.DataValue.create(customNameVisibleAccessor, visible)
+            )
+        )
+
+        player.sendPacket(Packet(packet))
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/DummyEntityFactory.kt

@@ -0,0 +1,15 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.internal.entities.EcoDummyEntity
+import com.willfp.eco.internal.spigot.proxy.DummyEntityFactoryProxy
+import org.bukkit.Location
+import org.bukkit.craftbukkit.CraftWorld
+import org.bukkit.entity.Entity
+import org.bukkit.entity.Zombie
+
+class DummyEntityFactory : DummyEntityFactoryProxy {
+    override fun createDummyEntity(location: Location): Entity {
+        val world = location.world as CraftWorld
+        return EcoDummyEntity(world.createEntity(location, Zombie::class.java))
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/EntityControllerFactory.kt

@@ -0,0 +1,12 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.core.entities.ai.EntityController
+import com.willfp.eco.internal.spigot.proxy.EntityControllerFactoryProxy
+import com.willfp.eco.internal.spigot.proxy.v1_21_5.entity.EcoEntityController
+import org.bukkit.entity.Mob
+
+class EntityControllerFactory : EntityControllerFactoryProxy {
+    override fun <T : Mob> createEntityController(entity: T): EntityController<T> {
+        return EcoEntityController(entity)
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/ExtendedPersistentDataContainerFactory.kt

@@ -0,0 +1,91 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.core.data.ExtendedPersistentDataContainer
+import com.willfp.eco.internal.spigot.proxy.ExtendedPersistentDataContainerFactoryProxy
+import net.minecraft.nbt.Tag
+import org.bukkit.Material
+import org.bukkit.craftbukkit.inventory.CraftItemStack
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataContainer
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataTypeRegistry
+import org.bukkit.inventory.ItemStack
+import org.bukkit.persistence.PersistentDataContainer
+import org.bukkit.persistence.PersistentDataType
+import java.lang.reflect.Field
+
+class ExtendedPersistentDataContainerFactory : ExtendedPersistentDataContainerFactoryProxy {
+    private val registry: CraftPersistentDataTypeRegistry
+
+    init {
+        /*
+         Can't grab actual instance since it's in CraftMetaItem (which is package-private)
+         And getting it would mean more janky reflection
+         */
+        val item = CraftItemStack.asCraftCopy(ItemStack(Material.STONE))
+        val pdc = item.itemMeta!!.persistentDataContainer
+
+        // Cross-version compatibility:
+        val registryField: Field = try {
+            CraftPersistentDataContainer::class.java.getDeclaredField("registry")
+        } catch (e: NoSuchFieldException) {
+            CraftPersistentDataContainer::class.java.superclass.getDeclaredField("registry")
+        }
+
+        this.registry = registryField
+            .apply { isAccessible = true }.get(pdc) as CraftPersistentDataTypeRegistry
+    }
+
+    override fun adapt(pdc: PersistentDataContainer): ExtendedPersistentDataContainer {
+        return when (pdc) {
+            is CraftPersistentDataContainer -> EcoPersistentDataContainer(pdc)
+            else -> throw IllegalArgumentException("Custom PDC instance ${pdc::class.java.name} is not supported!")
+        }
+    }
+
+    override fun newPdc(): PersistentDataContainer {
+        return CraftPersistentDataContainer(registry)
+    }
+
+    inner class EcoPersistentDataContainer(
+        private val handle: CraftPersistentDataContainer
+    ) : ExtendedPersistentDataContainer {
+        @Suppress("UNCHECKED_CAST")
+        private val customDataTags: MutableMap<String, Tag> =
+            CraftPersistentDataContainer::class.java.getDeclaredField("customDataTags")
+                .apply { isAccessible = true }.get(handle) as MutableMap<String, Tag>
+
+        override fun <T : Any, Z : Any> set(key: String, dataType: PersistentDataType<T, Z>, value: Z) {
+            customDataTags[key] =
+                registry.wrap(dataType, dataType.toPrimitive(value, handle.adapterContext))
+        }
+
+        override fun <T : Any, Z : Any> has(key: String, dataType: PersistentDataType<T, Z>): Boolean {
+            val value = customDataTags[key] ?: return false
+            return registry.isInstanceOf(dataType, value)
+        }
+
+        override fun <T : Any, Z : Any> get(key: String, dataType: PersistentDataType<T, Z>): Z? {
+            val value = customDataTags[key] ?: return null
+            return dataType.fromPrimitive(registry.extract<T, Tag>(dataType, value), handle.adapterContext)
+        }
+
+        override fun <T : Any, Z : Any> getOrDefault(
+            key: String,
+            dataType: PersistentDataType<T, Z>,
+            defaultValue: Z
+        ): Z {
+            return get(key, dataType) ?: defaultValue
+        }
+
+        override fun remove(key: String) {
+            customDataTags.remove(key)
+        }
+
+        override fun getAllKeys(): MutableSet<String> {
+            return customDataTags.keys
+        }
+
+        override fun getBase(): PersistentDataContainer {
+            return handle
+        }
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/FastItemStackFactory.kt

@@ -0,0 +1,13 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.core.fast.FastItemStack
+import com.willfp.eco.internal.spigot.proxy.FastItemStackFactoryProxy
+import com.willfp.eco.internal.spigot.proxy.common.modern.NewEcoFastItemStack
+import com.willfp.eco.internal.spigot.proxy.v1_21_5.item.NewerEcoFastItemStack
+import org.bukkit.inventory.ItemStack
+
+class FastItemStackFactory : FastItemStackFactoryProxy {
+    override fun create(itemStack: ItemStack): FastItemStack {
+        return NewerEcoFastItemStack(itemStack)
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/MiniMessageTranslator.kt

@@ -0,0 +1,33 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.core.display.Display
+import com.willfp.eco.internal.spigot.proxy.MiniMessageTranslatorProxy
+import com.willfp.eco.util.toLegacy
+import net.kyori.adventure.text.minimessage.MiniMessage
+
+class MiniMessageTranslator : MiniMessageTranslatorProxy {
+    override fun format(message: String): String {
+        var mut = message
+
+        val startsWithPrefix = mut.startsWith(Display.PREFIX)
+        if (startsWithPrefix) {
+            mut = mut.substring(2)
+        }
+
+        mut = mut.replace('§', '&')
+
+        val miniMessage = runCatching {
+            MiniMessage.miniMessage().deserialize(
+                mut
+            ).toLegacy()
+        }.getOrNull() ?: mut
+
+        mut = if (startsWithPrefix) {
+            Display.PREFIX + miniMessage
+        } else {
+            miniMessage
+        }
+
+        return mut
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/PacketHandler.kt

@@ -0,0 +1,46 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.core.EcoPlugin
+import com.willfp.eco.core.packet.PacketListener
+import com.willfp.eco.internal.spigot.proxy.PacketHandlerProxy
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.PacketHeldItemSlot
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.PacketSetSlot
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.clearFrames
+import com.willfp.eco.internal.spigot.proxy.v1_21_5.packet.NewItemsPacketOpenWindowMerchant
+import com.willfp.eco.internal.spigot.proxy.v1_21_5.packet.NewItemsPacketSetCreativeSlot
+import com.willfp.eco.internal.spigot.proxy.v1_21_5.packet.NewItemsPacketWindowItems
+import net.minecraft.network.protocol.Packet
+import org.bukkit.craftbukkit.entity.CraftPlayer
+import org.bukkit.entity.Player
+
+class PacketHandler : PacketHandlerProxy {
+    override fun sendPacket(player: Player, packet: com.willfp.eco.core.packet.Packet) {
+        if (player !is CraftPlayer) {
+            return
+        }
+
+        val handle = packet.handle
+
+        if (handle !is Packet<*>) {
+            return
+        }
+
+        player.handle.connection.send(handle)
+    }
+
+    override fun clearDisplayFrames() {
+        clearFrames()
+    }
+
+    override fun getPacketListeners(plugin: EcoPlugin): List<PacketListener> {
+        // No PacketAutoRecipe for 1.21.3+ because recipes have been changed internally
+
+        return listOf(
+            PacketHeldItemSlot,
+            NewItemsPacketOpenWindowMerchant,
+            NewItemsPacketSetCreativeSlot,
+            PacketSetSlot,
+            NewItemsPacketWindowItems(plugin)
+        )
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/SNBTConverter.kt

@@ -0,0 +1,81 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.mojang.serialization.Dynamic
+import com.willfp.eco.core.items.TestableItem
+import com.willfp.eco.core.recipe.parts.EmptyTestableItem
+import com.willfp.eco.internal.spigot.proxy.SNBTConverterProxy
+import net.minecraft.nbt.CompoundTag
+import net.minecraft.nbt.NbtOps
+import net.minecraft.nbt.SnbtPrinterTagVisitor
+import net.minecraft.nbt.TagParser
+import net.minecraft.server.MinecraftServer
+import net.minecraft.util.datafix.fixes.References
+import org.bukkit.Bukkit
+import org.bukkit.craftbukkit.CraftServer
+import org.bukkit.craftbukkit.inventory.CraftItemStack
+import org.bukkit.craftbukkit.util.CraftMagicNumbers
+import org.bukkit.inventory.ItemStack
+
+private val registryAccess = (Bukkit.getServer() as CraftServer).server.registryAccess()
+
+class SNBTConverter : SNBTConverterProxy {
+    private fun parseItemSNBT(snbt: String): CompoundTag? {
+        val nbt = runCatching { TagParser.parseCompoundFully(snbt) }.getOrNull() ?: return null
+        val dataVersion = if (nbt.contains("DataVersion")) {
+            nbt.getInt("DataVersion").get()
+        } else null
+
+        // If the data version is the same as the server's data version, we don't need to fix it
+
+        if (dataVersion == CraftMagicNumbers.INSTANCE.dataVersion) {
+            return nbt
+        }
+
+        return MinecraftServer.getServer().fixerUpper.update(
+            References.ITEM_STACK,
+            Dynamic(NbtOps.INSTANCE, nbt),
+            dataVersion ?: 3700, // 3700 is the 1.20.4 data version
+            CraftMagicNumbers.INSTANCE.dataVersion
+        ).value as CompoundTag
+    }
+
+    override fun fromSNBT(snbt: String): ItemStack? {
+        val tag = parseItemSNBT(snbt) ?: return null
+        val nms = net.minecraft.world.item.ItemStack.parse(registryAccess, tag).orElse(null) ?: return null
+        return CraftItemStack.asBukkitCopy(nms)
+    }
+
+    override fun toSNBT(itemStack: ItemStack): String {
+        val nms = CraftItemStack.asNMSCopy(itemStack)
+        val tag = nms.save(registryAccess) as CompoundTag
+        tag.putInt("DataVersion", CraftMagicNumbers.INSTANCE.dataVersion)
+        return SnbtPrinterTagVisitor().visit(tag)
+    }
+
+    override fun makeSNBTTestable(snbt: String): TestableItem {
+        val tag = parseItemSNBT(snbt) ?: return EmptyTestableItem()
+        val nms = net.minecraft.world.item.ItemStack.parse(registryAccess, tag).orElse(null)
+            ?: return EmptyTestableItem()
+
+        tag.remove("Count")
+        return SNBTTestableItem(CraftItemStack.asBukkitCopy(nms), tag)
+    }
+
+    class SNBTTestableItem(
+        private val item: ItemStack,
+        private val tag: CompoundTag
+    ) : TestableItem {
+        override fun matches(itemStack: ItemStack?): Boolean {
+            if (itemStack == null) {
+                return false
+            }
+
+            val nms = CraftItemStack.asNMSCopy(itemStack)
+            val nmsTag = nms.save(registryAccess) as CompoundTag
+            nmsTag.remove("Count")
+            return tag.copy().merge(nmsTag) == nmsTag && itemStack.type == item.type
+        }
+
+        override fun getItem(): ItemStack = item
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/Skull.kt

@@ -0,0 +1,18 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.internal.spigot.proxy.SkullProxy
+import com.willfp.eco.internal.spigot.proxy.common.modern.texture
+import org.bukkit.inventory.meta.SkullMeta
+
+class Skull : SkullProxy {
+    override fun setSkullTexture(
+        meta: SkullMeta,
+        base64: String
+    ) {
+        meta.texture = base64
+    }
+
+    override fun getSkullTexture(
+        meta: SkullMeta
+    ): String? = meta.texture
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/TPS.kt

@@ -0,0 +1,11 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5
+
+import com.willfp.eco.internal.spigot.proxy.TPSProxy
+import org.bukkit.Bukkit
+import org.bukkit.craftbukkit.CraftServer
+
+class TPS : TPSProxy {
+    override fun getTPS(): Double {
+        return (Bukkit.getServer() as CraftServer).handle.server.tps1.average
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/entity/EcoEntityController.kt

@@ -0,0 +1,95 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5.entity
+
+import com.willfp.eco.core.entities.ai.CustomGoal
+import com.willfp.eco.core.entities.ai.EntityController
+import com.willfp.eco.core.entities.ai.EntityGoal
+import com.willfp.eco.core.entities.ai.TargetGoal
+import com.willfp.eco.internal.spigot.proxy.common.ai.CustomGoalFactory
+import com.willfp.eco.internal.spigot.proxy.common.ai.getGoalFactory
+import com.willfp.eco.internal.spigot.proxy.common.toPathfinderMob
+import net.minecraft.world.entity.PathfinderMob
+import net.minecraft.world.entity.ai.goal.Goal
+import org.bukkit.entity.Mob
+
+class EcoEntityController<T : Mob>(
+    private val handle: T
+) : EntityController<T> {
+    override fun addEntityGoal(priority: Int, goal: EntityGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        nms.goalSelector.addGoal(
+            priority,
+            goal.getGoalFactory()?.create(goal, nms) ?: return this
+        )
+
+        return this
+    }
+
+    override fun removeEntityGoal(goal: EntityGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        val predicate: (Goal) -> Boolean = if (goal is CustomGoal<*>) {
+            { CustomGoalFactory.isGoalOfType(it, goal) }
+        } else {
+            { goal.getGoalFactory()?.isGoalOfType(it) == true }
+        }
+
+        for (wrapped in nms.goalSelector.availableGoals.toSet()) {
+            if (predicate(wrapped.goal)) {
+                nms.goalSelector.removeGoal(wrapped.goal)
+            }
+        }
+
+        return this
+    }
+
+    override fun clearEntityGoals(): EntityController<T> {
+        val nms = getNms() ?: return this
+        nms.goalSelector.availableGoals.clear()
+        return this
+    }
+
+    override fun addTargetGoal(priority: Int, goal: TargetGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        nms.targetSelector.addGoal(
+            priority, goal.getGoalFactory()?.create(goal, nms) ?: return this
+        )
+
+        nms.targetSelector
+
+        return this
+    }
+
+    override fun removeTargetGoal(goal: TargetGoal<in T>): EntityController<T> {
+        val nms = getNms() ?: return this
+
+        val predicate: (Goal) -> Boolean = if (goal is CustomGoal<*>) {
+            { CustomGoalFactory.isGoalOfType(it, goal) }
+        } else {
+            { goal.getGoalFactory()?.isGoalOfType(it) == true }
+        }
+
+        for (wrapped in nms.targetSelector.availableGoals.toSet()) {
+            if (predicate(wrapped.goal)) {
+                nms.targetSelector.removeGoal(wrapped.goal)
+            }
+        }
+
+        return this
+    }
+
+    override fun clearTargetGoals(): EntityController<T> {
+        val nms = getNms() ?: return this
+        nms.targetSelector.availableGoals.clear()
+        return this
+    }
+
+    private fun getNms(): PathfinderMob? {
+        return handle.toPathfinderMob()
+    }
+
+    override fun getEntity(): T {
+        return handle
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/item/NewerEcoFastItemStack.kt

@@ -0,0 +1,185 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5.item
+
+import com.willfp.eco.internal.spigot.proxy.common.modern.NewEcoFastItemStack
+import net.minecraft.core.component.DataComponents
+import net.minecraft.world.item.component.TooltipDisplay
+import org.bukkit.inventory.ItemFlag
+import org.bukkit.inventory.ItemStack
+
+
+open class NewerEcoFastItemStack(
+    bukkit: ItemStack,
+) : NewEcoFastItemStack(bukkit) {
+    override fun addItemFlags(vararg hideFlags: ItemFlag) {
+        for (flag in hideFlags) {
+            when (flag) {
+                ItemFlag.HIDE_ENCHANTS -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.ENCHANTMENTS, true)
+                    }
+                }
+
+                ItemFlag.HIDE_ATTRIBUTES -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.ATTRIBUTE_MODIFIERS, true)
+                    }
+                }
+
+                ItemFlag.HIDE_UNBREAKABLE -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.UNBREAKABLE, true)
+                    }
+                }
+
+                ItemFlag.HIDE_DESTROYS -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.CAN_BREAK, true)
+                    }
+                }
+
+                ItemFlag.HIDE_PLACED_ON -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.CAN_PLACE_ON, true)
+                    }
+                }
+
+                ItemFlag.HIDE_ADDITIONAL_TOOLTIP -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        TooltipDisplay(true, tooltip.hiddenComponents)
+                    }
+                }
+
+                ItemFlag.HIDE_DYE -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.DYED_COLOR, true)
+                    }
+                }
+
+                ItemFlag.HIDE_ARMOR_TRIM -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.TRIM, true)
+                    }
+                }
+
+                ItemFlag.HIDE_STORED_ENCHANTS -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.STORED_ENCHANTMENTS, true)
+                    }
+                }
+            }
+        }
+
+        apply()
+    }
+
+    override fun removeItemFlags(vararg hideFlags: ItemFlag) {
+        for (flag in hideFlags) {
+            when (flag) {
+                ItemFlag.HIDE_ENCHANTS -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.ENCHANTMENTS, false)
+                    }
+                }
+
+                ItemFlag.HIDE_ATTRIBUTES -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.ATTRIBUTE_MODIFIERS, false)
+                    }
+                }
+
+                ItemFlag.HIDE_UNBREAKABLE -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.UNBREAKABLE, false)
+                    }
+                }
+
+                ItemFlag.HIDE_DESTROYS -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.CAN_BREAK, false)
+                    }
+                }
+
+                ItemFlag.HIDE_PLACED_ON -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.CAN_PLACE_ON, false)
+                    }
+                }
+
+                ItemFlag.HIDE_ADDITIONAL_TOOLTIP -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        TooltipDisplay(false, tooltip.hiddenComponents)
+                    }
+                }
+
+                ItemFlag.HIDE_DYE -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.DYED_COLOR, false)
+                    }
+                }
+
+                ItemFlag.HIDE_ARMOR_TRIM -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.TRIM, false)
+                    }
+                }
+
+                ItemFlag.HIDE_STORED_ENCHANTS -> {
+                    handle.modifyComponent(DataComponents.TOOLTIP_DISPLAY) { tooltip ->
+                        tooltip.withHidden(DataComponents.STORED_ENCHANTMENTS, false)
+                    }
+                }
+            }
+        }
+
+        apply()
+    }
+
+    override fun hasItemFlag(flag: ItemFlag): Boolean {
+        return when (flag) {
+            ItemFlag.HIDE_ENCHANTS -> {
+                val tooltip = handle.get(DataComponents.TOOLTIP_DISPLAY) ?: return false
+                !tooltip.shows(DataComponents.ENCHANTMENTS)
+            }
+
+            ItemFlag.HIDE_ATTRIBUTES -> {
+                val tooltip = handle.get(DataComponents.TOOLTIP_DISPLAY) ?: return false
+                !tooltip.shows(DataComponents.ATTRIBUTE_MODIFIERS)
+            }
+
+            ItemFlag.HIDE_UNBREAKABLE -> {
+                val tooltip = handle.get(DataComponents.TOOLTIP_DISPLAY) ?: return false
+                !tooltip.shows(DataComponents.UNBREAKABLE)
+            }
+
+            ItemFlag.HIDE_DESTROYS -> {
+                val tooltip = handle.get(DataComponents.TOOLTIP_DISPLAY) ?: return false
+                !tooltip.shows(DataComponents.CAN_BREAK)
+            }
+
+            ItemFlag.HIDE_PLACED_ON -> {
+                val tooltip = handle.get(DataComponents.TOOLTIP_DISPLAY) ?: return false
+                !tooltip.shows(DataComponents.CAN_PLACE_ON)
+            }
+
+            ItemFlag.HIDE_ADDITIONAL_TOOLTIP -> {
+                val tooltip = handle.get(DataComponents.TOOLTIP_DISPLAY) ?: return false
+                tooltip.hideTooltip
+            }
+
+            ItemFlag.HIDE_DYE -> {
+                val tooltip = handle.get(DataComponents.TOOLTIP_DISPLAY) ?: return false
+                !tooltip.shows(DataComponents.DYED_COLOR)
+            }
+
+            ItemFlag.HIDE_ARMOR_TRIM -> {
+                val tooltip = handle.get(DataComponents.TOOLTIP_DISPLAY) ?: return false
+                !tooltip.shows(DataComponents.TRIM)
+            }
+
+            ItemFlag.HIDE_STORED_ENCHANTS -> {
+                val tooltip = handle.get(DataComponents.TOOLTIP_DISPLAY) ?: return false
+                !tooltip.shows(DataComponents.STORED_ENCHANTMENTS)
+            }
+        }
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/packet/NewItemsPacketOpenWindowMerchant.kt

@@ -0,0 +1,35 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5.packet
+
+import com.willfp.eco.core.display.Display
+import com.willfp.eco.core.packet.PacketEvent
+import com.willfp.eco.core.packet.PacketListener
+import com.willfp.eco.internal.spigot.proxy.common.asBukkitStack
+import net.minecraft.network.protocol.game.ClientboundMerchantOffersPacket
+import net.minecraft.world.item.trading.MerchantOffers
+
+object NewItemsPacketOpenWindowMerchant : PacketListener {
+    private val field = ClientboundMerchantOffersPacket::class.java
+        .declaredFields
+        .first { it.type == MerchantOffers::class.java }
+        .apply { isAccessible = true }
+
+    override fun onSend(event: PacketEvent) {
+        val packet = event.packet.handle as? ClientboundMerchantOffersPacket ?: return
+
+        val offers = MerchantOffers()
+
+        for (offer in packet.offers) {
+            val new = offer.copy()
+
+            Display.display(new.baseCostA.itemStack.asBukkitStack(), event.player)
+            if (new.costB.isPresent) {
+                Display.display(new.costB.get().itemStack.asBukkitStack(), event.player)
+            }
+            Display.display(new.result.asBukkitStack(), event.player)
+
+            offers += new
+        }
+
+        field.set(packet, offers)
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/packet/NewItemsPacketSetCreativeSlot.kt

@@ -0,0 +1,19 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5.packet
+
+import com.willfp.eco.core.display.Display
+import com.willfp.eco.core.packet.PacketEvent
+import com.willfp.eco.core.packet.PacketListener
+import com.willfp.eco.internal.spigot.proxy.common.asBukkitStack
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.DisplayFrame
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.lastDisplayFrame
+import net.minecraft.network.protocol.game.ServerboundSetCreativeModeSlotPacket
+
+object NewItemsPacketSetCreativeSlot : PacketListener {
+    override fun onReceive(event: PacketEvent) {
+        val packet = event.packet.handle as? ServerboundSetCreativeModeSlotPacket ?: return
+
+        Display.revert(packet.itemStack.asBukkitStack())
+
+        event.player.lastDisplayFrame = DisplayFrame.EMPTY
+    }
+}

eco-core/core-nms/v1_21_5/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_5/packet/NewItemsPacketWindowItems.kt

@@ -0,0 +1,52 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_5.packet
+
+import com.willfp.eco.core.EcoPlugin
+import com.willfp.eco.core.display.Display
+import com.willfp.eco.core.packet.PacketEvent
+import com.willfp.eco.internal.spigot.proxy.common.asBukkitStack
+import com.willfp.eco.internal.spigot.proxy.common.asNMSStack
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.PacketWindowItems
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.DisplayFrame
+import com.willfp.eco.internal.spigot.proxy.common.packet.display.frame.lastDisplayFrame
+import net.minecraft.network.protocol.game.ClientboundContainerSetContentPacket
+import java.util.UUID
+import java.util.concurrent.ConcurrentHashMap
+
+class NewItemsPacketWindowItems(
+    plugin: EcoPlugin
+) : PacketWindowItems(plugin) {
+    private val lastKnownWindowIDs = ConcurrentHashMap<UUID, Int>()
+
+    override fun onSend(event: PacketEvent) {
+        val packet = event.packet.handle as? ClientboundContainerSetContentPacket ?: return
+        val player = event.player
+
+        Display.display(packet.carriedItem.asBukkitStack(), player)
+
+        val windowId = packet.containerId
+
+        val lastKnownID = lastKnownWindowIDs[player.uniqueId]
+        lastKnownWindowIDs[player.uniqueId] = windowId
+
+        // If there is any change in window ID at any point,
+        // Remove the last display frame to prevent any potential conflicts.
+        // If the window ID is not zero (not a player inventory), then remove too,
+        // as GUIs are not player inventories.
+        if (lastKnownID != windowId || windowId != 0) {
+            player.lastDisplayFrame = DisplayFrame.EMPTY
+        }
+
+        val itemStacks = packet.items.map { it.asBukkitStack() }
+
+        val newItems = modifyWindowItems(itemStacks.toMutableList(), windowId, player)
+
+        val newPacket = ClientboundContainerSetContentPacket(
+            packet.containerId,
+            packet.stateId,
+            newItems.map { it.asNMSStack() },
+            packet.carriedItem,
+        )
+
+        event.packet.handle = newPacket
+    }
+}

eco-core/core-nms/v1_21_6/build.gradle.kts

@@ -0,0 +1,52 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
+plugins {
+    id("io.papermc.paperweight.userdev")
+}
+
+group = "com.willfp"
+version = rootProject.version
+
+dependencies {
+    implementation(project(":eco-core:core-nms:modern"))
+    implementation(project(":eco-core:core-nms:common"))
+    paperweight.paperDevBundle("1.21.6-R0.1-SNAPSHOT")
+
+    implementation("net.kyori:adventure-text-minimessage:4.11.0") {
+        version {
+            strictly("4.11.0")
+        }
+        exclude(group = "net.kyori", module = "adventure-api")
+    }
+}
+
+tasks {
+    build {
+        dependsOn(reobfJar)
+    }
+
+    reobfJar {
+        mustRunAfter(shadowJar)
+    }
+
+    shadowJar {
+        relocate(
+            "com.willfp.eco.internal.spigot.proxy.common",
+            "com.willfp.eco.internal.spigot.proxy.v1_21_6.common"
+        )
+        relocate(
+            "net.kyori.adventure.text.minimessage",
+            "com.willfp.eco.internal.spigot.proxy.v1_21_6.minimessage"
+        )
+    }
+
+    compileJava {
+        options.release.set(21)
+    }
+
+    compileKotlin {
+        compilerOptions {
+            jvmTarget.set(JvmTarget.JVM_21)
+        }
+    }
+}

eco-core/core-nms/v1_21_6/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_6/BukkitCommands.kt

@@ -0,0 +1,35 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_6
+
+import com.willfp.eco.core.command.PluginCommandBase
+import com.willfp.eco.internal.spigot.proxy.BukkitCommandsProxy
+import org.bukkit.Bukkit
+import org.bukkit.command.Command
+import org.bukkit.command.SimpleCommandMap
+import org.bukkit.craftbukkit.CraftServer
+import java.lang.reflect.Field
+
+class BukkitCommands : BukkitCommandsProxy {
+    private val knownCommandsField: Field by lazy {
+        SimpleCommandMap::class.java.getDeclaredField("knownCommands")
+            .apply {
+                isAccessible = true
+            }
+    }
+
+    @Suppress("UNCHECKED_CAST")
+    private val knownCommands: MutableMap<String, Command>
+        get() = knownCommandsField.get(getCommandMap()) as MutableMap<String, Command>
+
+    override fun getCommandMap(): SimpleCommandMap {
+        return (Bukkit.getServer() as CraftServer).commandMap
+    }
+
+    override fun syncCommands() {
+        (Bukkit.getServer() as CraftServer).syncCommands()
+    }
+
+    override fun unregisterCommand(command: PluginCommandBase) {
+        knownCommands.remove(command.name)
+        knownCommands.remove("${command.plugin.name.lowercase()}:${command.name}")
+    }
+}

eco-core/core-nms/v1_21_6/src/main/kotlin/com/willfp/eco/internal/spigot/proxy/v1_21_6/CommonsInitializer.kt

@@ -0,0 +1,172 @@
+package com.willfp.eco.internal.spigot.proxy.v1_21_6
+
+import ca.spottedleaf.dataconverter.minecraft.MCDataConverter
+import com.willfp.eco.core.EcoPlugin
+import com.willfp.eco.internal.spigot.proxy.CommonsInitializerProxy
+import com.willfp.eco.internal.spigot.proxy.common.CommonsProvider
+import com.willfp.eco.internal.spigot.proxy.common.packet.PacketInjectorListener
+import com.willfp.eco.internal.spigot.proxy.common.toResourceLocation
+import io.papermc.paper.adventure.PaperAdventure
+import net.kyori.adventure.text.Component
+import net.kyori.adventure.text.serializer.json.JSONComponentSerializer
+import net.minecraft.core.component.DataComponents
+import net.minecraft.core.registries.BuiltInRegistries
+import net.minecraft.nbt.CompoundTag
+import net.minecraft.nbt.Tag
+import net.minecraft.network.chat.ComponentSerialization
+import net.minecraft.resources.ResourceLocation
+import net.minecraft.server.level.ServerPlayer
+import net.minecraft.world.entity.PathfinderMob
+import net.minecraft.world.item.Item
+import org.bukkit.Bukkit
+import org.bukkit.Material
+import org.bukkit.NamespacedKey
+import org.bukkit.craftbukkit.CraftServer
+import org.bukkit.craftbukkit.entity.CraftEntity
+import org.bukkit.craftbukkit.entity.CraftMob
+import org.bukkit.craftbukkit.entity.CraftPlayer
+import org.bukkit.craftbukkit.inventory.CraftItemStack
+import org.bukkit.craftbukkit.inventory.CraftMetaArmor
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataContainer
+import org.bukkit.craftbukkit.persistence.CraftPersistentDataTypeRegistry
+import org.bukkit.craftbukkit.util.CraftMagicNumbers
+import org.bukkit.craftbukkit.util.CraftNamespacedKey
+import org.bukkit.entity.LivingEntity
+import org.bukkit.entity.Mob
+import org.bukkit.entity.Player
+import org.bukkit.inventory.ItemStack
+import org.bukkit.persistence.PersistentDataContainer
+import java.lang.reflect.Field
+
+class CommonsInitializer : CommonsInitializerProxy {
+    override fun init(plugin: EcoPlugin) {
+        CommonsProvider.setIfNeeded(CommonsProviderImpl)
+        plugin.onEnable {
+            plugin.eventManager.registerListener(PacketInjectorListener)
+        }
+    }
+
+    object CommonsProviderImpl : CommonsProvider {
+        private val cisHandle: Field = CraftItemStack::class.java.getDeclaredField("handle").apply {
+            isAccessible = true
+        }
+
+        private val pdcRegsitry = CraftMetaArmor::class.java
+            .superclass // Access CraftMetaItem
+            .getDeclaredField("DATA_TYPE_REGISTRY")
+            .apply { isAccessible = true }
+            .get(null) as CraftPersistentDataTypeRegistry
+
+        override val nbtTagString = 8
+
+        override fun toPathfinderMob(mob: Mob): PathfinderMob? {
+            val craft = mob as? CraftMob ?: return null
+            return craft.handle as? PathfinderMob
+        }
+
+        override fun toResourceLocation(namespacedKey: NamespacedKey): ResourceLocation =
+            CraftNamespacedKey.toMinecraft(namespacedKey)
+
+        override fun asNMSStack(itemStack: ItemStack): net.minecraft.world.item.ItemStack {
+            return if (itemStack !is CraftItemStack) {
+                CraftItemStack.asNMSCopy(itemStack)
+            } else {
+                cisHandle[itemStack] as net.minecraft.world.item.ItemStack? ?: CraftItemStack.asNMSCopy(itemStack)
+            }
+        }
+
+        override fun asBukkitStack(itemStack: net.minecraft.world.item.ItemStack): ItemStack {
+            return CraftItemStack.asCraftMirror(itemStack)
+        }
+
+        override fun mergeIfNeeded(itemStack: ItemStack, nmsStack: net.minecraft.world.item.ItemStack) {
+            if (itemStack !is CraftItemStack) {
+                itemStack.itemMeta = CraftItemStack.asCraftMirror(nmsStack).itemMeta
+            }
+        }
+
+        override fun toBukkitEntity(entity: net.minecraft.world.entity.LivingEntity): LivingEntity? =
+            CraftEntity.getEntity(Bukkit.getServer() as CraftServer, entity) as? LivingEntity
+
+        override fun makePdc(tag: CompoundTag, base: Boolean): PersistentDataContainer {
+            fun emptyPdc(): CraftPersistentDataContainer = CraftPersistentDataContainer(pdcRegsitry)
+
+            fun CompoundTag?.toPdc(): PersistentDataContainer {
+                val pdc = emptyPdc()
+                this ?: return pdc
+                val keys = this.keySet()
+                for (key in keys) {
+                    pdc.put(key, this[key])
+                }
+
+                return pdc
+            }
+
+            return if (base) {
+                tag.toPdc()
+            } else {
+                if (tag.contains("PublicBukkitValues")) {
+                    tag.getCompound("PublicBukkitValues").get().toPdc()
+                } else {
+                    emptyPdc()
+                }
+            }
+        }
+
+        override fun setPdc(
+            tag: CompoundTag,
+            pdc: PersistentDataContainer?,
+            item: net.minecraft.world.item.ItemStack?
+        ) {
+            fun CraftPersistentDataContainer.toTag(): CompoundTag {
+                val compound = CompoundTag()
+                val rawPublicMap: Map<String, Tag> = this.raw
+                for ((key, value) in rawPublicMap) {
+                    compound.put(key, value)
+                }
+
+                return compound
+            }
+
+            val container = when (pdc) {
+                is CraftPersistentDataContainer? -> pdc
+                else -> null
+            }
+
+            if (item != null) {
+                if (container != null && !container.isEmpty) {
+                    for (key in tag.keySet()) {
+                        tag.remove(key)
+                    }
+
+                    tag.merge(container.toTag())
+                } else {
+                    item.remove(DataComponents.CUSTOM_DATA)
+                }
+            } else {
+                if (container != null && !container.isEmpty) {
+                    tag.put("PublicBukkitValues", container.toTag())
+                } else {
+                    tag.remove("PublicBukkitValues")
+                }
+            }
+        }
+
+        override fun materialToItem(material: Material): Item =
+            BuiltInRegistries.ITEM.getOptional(material.key.toResourceLocation())
+                .orElseThrow { IllegalArgumentException("Material is not item!") }
+
+        override fun itemToMaterial(item: Item) =
+            Material.getMaterial(BuiltInRegistries.ITEM.getKey(item).path.uppercase())
+                ?: throw IllegalArgumentException("Invalid material!")
+
+        override fun toNMS(player: Player): ServerPlayer {
+            return (player as CraftPlayer).handle
+        }
+
+        override fun toNMS(component: Component): net.minecraft.network.chat.Component {
+            // TODO: Don't have hard dependency on paper
+            return PaperAdventure.asVanilla(component)
+        }
+    }
+}