diff --git a/adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedForcedDatapack.java b/adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedForcedDatapack.java
index e5555f39b..ff4d78ce0 100644
--- a/adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedForcedDatapack.java
+++ b/adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedForcedDatapack.java
@@ -315,11 +315,11 @@ public final class ModdedForcedDatapack {
             throw new IllegalStateException("SHA-256 is unavailable", missing);
         }
         digest.update((HASH_SALT + '|' + ModdedEngineBootstrap.loader().platformName()
-                + '|' + DataVersion.V26_2.getPackFormat() + '\n').getBytes(StandardCharsets.UTF_8));
+                + '|' + DataVersion.V26_3.getPackFormat() + '\n').getBytes(StandardCharsets.UTF_8));
         String inputFingerprint = IrisDatapackCompiler.computeInputFingerprint(
                 compilationPackRoots(),
                 List.of(),
-                DataVersion.V26_2.get(),
+                DataVersion.V26_3.get(),
                 false
         );
         digest.update(inputFingerprint.getBytes(StandardCharsets.UTF_8));
@@ -328,7 +328,7 @@ public final class ModdedForcedDatapack {
 
     private static void writeStagedPack(Path stagingDirectory) throws IOException {
         Map<String, KSet<String>> seenBiomes = new LinkedHashMap<>();
-        IDataFixer fixer = DataVersion.V26_2.get();
+        IDataFixer fixer = DataVersion.V26_3.get();
 
         int packCount = 0;
         KList<String> presetIds = new KList<>();
@@ -679,7 +679,7 @@ public final class ModdedForcedDatapack {
     }
 
     static void writePackMeta(Path packDirectory) throws IOException {
-        int packFormat = DataVersion.V26_2.getPackFormat();
+        int packFormat = DataVersion.V26_3.getPackFormat();
         String json = "{\n"
                 + "  \"pack\": {\n"
                 + "    \"description\": \"Iris world generation biomes and dimension types for installed packs.\",\n"
diff --git a/adapters/modded-common/src/main/java/art/arcane/iris/modded/WorldCheckDimensionContract.java b/adapters/modded-common/src/main/java/art/arcane/iris/modded/WorldCheckDimensionContract.java
index 3fcf5e4c0..1ee890883 100644
--- a/adapters/modded-common/src/main/java/art/arcane/iris/modded/WorldCheckDimensionContract.java
+++ b/adapters/modded-common/src/main/java/art/arcane/iris/modded/WorldCheckDimensionContract.java
@@ -55,7 +55,7 @@ final class WorldCheckDimensionContract {
     }
 
     static Dimension expectedDimensionContract(IrisDimension dimension) {
-        JSONObject json = new JSONObject(dimension.getDimensionType().toJson(DataVersion.V26_2.get()));
+        JSONObject json = new JSONObject(dimension.getDimensionType().toJson(DataVersion.V26_3.get()));
         return new Dimension(
                 json.getInt("min_y"),
                 json.getInt("height"),
diff --git a/adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedDatapackCommands.java b/adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedDatapackCommands.java
index ddb84d22f..f58722f51 100644
--- a/adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedDatapackCommands.java
+++ b/adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedDatapackCommands.java
@@ -165,7 +165,7 @@ public final class ModdedDatapackCommands {
             IrisDimension dimension = engine.getDimension();
             String json;
             try {
-                json = dimension.getDimensionType().toJson(DataVersion.V26_2.get());
+                json = dimension.getDimensionType().toJson(DataVersion.V26_3.get());
             } catch (Throwable e) {
                 ModdedIrisLog.error("Iris dimension type generation failed for {}", dimension.getLoadKey(), e);
                 IrisModdedCommands.fail(source, IrisLanguage.plain(ModdedCommandMessages.MODDED_DATAPACK_COMMANDS_DIMENSION_TYPE_GENERATION_FAILED, MessageArgument.untrusted("value", level.name()), MessageArgument.untrusted("value2", String.valueOf(e.getMessage()))));
@@ -187,7 +187,7 @@ public final class ModdedDatapackCommands {
         }
 
         File mcmeta = new File(worldDatapacksFolder(server), WORLD_PACK_NAME + "/pack.mcmeta");
-        int packFormat = DataVersion.V26_2.getPackFormat();
+        int packFormat = DataVersion.V26_3.getPackFormat();
         String meta = "{\n"
                 + "  \"pack\": {\n"
                 + "    \"description\": \"Iris dimension types derived from the installed Iris packs.\",\n"
diff --git a/adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedPregenMethod.java b/adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedPregenMethod.java
index 058066888..f61043f5a 100644
--- a/adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedPregenMethod.java
+++ b/adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedPregenMethod.java
@@ -503,7 +503,7 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
     /**
      * A dedicated server with {@code pause-when-empty-seconds > 0} returns from
      * {@code MinecraftServer#tickServer} before {@code tickChildren} once it has been empty for that
-     * long (26.2 only keeps {@code tickConnection} plus the task/chunk-poll window alive). That
+     * long (26.3 only keeps {@code tickConnection} plus the task/chunk-poll window alive). That
      * freezes every per-tick Iris service - world manager, scheduler, protocol sync, pregen HUD - and
      * the loader's own generation hooks for the whole job, and console pregen on a default
      * server.properties is always empty. The guard zeroes the setting for the duration of the job
diff --git a/adapters/modded-common/src/test/java/art/arcane/iris/modded/IrisModdedChunkGeneratorSpawnTest.java b/adapters/modded-common/src/test/java/art/arcane/iris/modded/IrisModdedChunkGeneratorSpawnTest.java
index a908898f3..43aa6b0a0 100644
--- a/adapters/modded-common/src/test/java/art/arcane/iris/modded/IrisModdedChunkGeneratorSpawnTest.java
+++ b/adapters/modded-common/src/test/java/art/arcane/iris/modded/IrisModdedChunkGeneratorSpawnTest.java
@@ -6,6 +6,7 @@ import net.minecraft.SharedConstants;
 import net.minecraft.server.Bootstrap;
 import net.minecraft.util.random.Weighted;
 import net.minecraft.util.random.WeightedList;
+import net.minecraft.util.valueproviders.UniformInt;
 import net.minecraft.world.entity.EntityTypes;
 import net.minecraft.world.level.biome.MobSpawnSettings;
 import org.junit.Test;
@@ -24,10 +25,10 @@ public class IrisModdedChunkGeneratorSpawnTest {
 
     @Test
     public void explicitSpawnsReplaceMatchingVanillaTypesAndPreserveOthers() {
-        MobSpawnSettings.SpawnerData zombie = new MobSpawnSettings.SpawnerData(EntityTypes.ZOMBIE, 1, 4);
-        MobSpawnSettings.SpawnerData vanillaSlime = new MobSpawnSettings.SpawnerData(EntityTypes.SLIME, 1, 1);
-        MobSpawnSettings.SpawnerData explicitSlime = new MobSpawnSettings.SpawnerData(EntityTypes.SLIME, 2, 5);
-        MobSpawnSettings.SpawnerData explicitCow = new MobSpawnSettings.SpawnerData(EntityTypes.COW, 2, 4);
+        MobSpawnSettings.SpawnerData zombie = new MobSpawnSettings.SpawnerData(EntityTypes.ZOMBIE, UniformInt.of(1, 4));
+        MobSpawnSettings.SpawnerData vanillaSlime = new MobSpawnSettings.SpawnerData(EntityTypes.SLIME, UniformInt.of(1, 1));
+        MobSpawnSettings.SpawnerData explicitSlime = new MobSpawnSettings.SpawnerData(EntityTypes.SLIME, UniformInt.of(2, 5));
+        MobSpawnSettings.SpawnerData explicitCow = new MobSpawnSettings.SpawnerData(EntityTypes.COW, UniformInt.of(2, 4));
         WeightedList<MobSpawnSettings.SpawnerData> vanilla = WeightedList.of(List.of(
                 new Weighted<>(zombie, 100),
                 new Weighted<>(vanillaSlime, 1)));
diff --git a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedDimensionTypeParityTest.java b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedDimensionTypeParityTest.java
index 1adc60d53..0f522dc2f 100644
--- a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedDimensionTypeParityTest.java
+++ b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedDimensionTypeParityTest.java
@@ -79,7 +79,7 @@ public class ModdedDimensionTypeParityTest {
         IrisDimension end = dimension("the_end", IrisEnvironment.THE_END, 0, 256, 256, new IrisDimensionTypeOptions());
         IrisDimension custom = dimension("custom_contract", IrisEnvironment.CUSTOM, -128, 384, 384, customOptions);
         List<IrisDimension> dimensions = List.of(overworld, nether, end, custom);
-        IDataFixer fixer = DataVersion.V26_2.get();
+        IDataFixer fixer = DataVersion.V26_3.get();
         Path packDirectory = Files.createTempDirectory("iris-dimension-contracts");
         KList<File> roots = new KList<>();
         roots.add(packDirectory.toFile());
diff --git a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedForcedDatapackTest.java b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedForcedDatapackTest.java
index beccd3958..ad1af8e24 100644
--- a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedForcedDatapackTest.java
+++ b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedForcedDatapackTest.java
@@ -51,15 +51,15 @@ import static org.junit.Assert.assertTrue;
 
 public class ModdedForcedDatapackTest {
     @Test
-    public void metadataRetains262FormatWhenBukkitAlsoSupports263() throws IOException {
+    public void metadataUses263DataFormat() throws IOException {
         Path packDirectory = Files.createTempDirectory("iris-modded-pack-format");
         try {
             ModdedForcedDatapack.writePackMeta(packDirectory);
             JSONObject pack = new JSONObject(Files.readString(packDirectory.resolve("pack.mcmeta")))
                     .getJSONObject("pack");
-            assertEquals(107, pack.getInt("pack_format"));
-            assertEquals(107, pack.getInt("min_format"));
-            assertEquals(107, pack.getInt("max_format"));
+            assertEquals(121, pack.getInt("pack_format"));
+            assertEquals(121, pack.getInt("min_format"));
+            assertEquals(121, pack.getInt("max_format"));
         } finally {
             deleteTree(packDirectory);
         }
diff --git a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedPlatformPathsTest.java b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedPlatformPathsTest.java
index facc55cf2..00009e7b1 100644
--- a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedPlatformPathsTest.java
+++ b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedPlatformPathsTest.java
@@ -33,7 +33,7 @@ public class ModdedPlatformPathsTest {
 
             @Override
             public String minecraftVersion() {
-                return "26.2";
+                return "26.3";
             }
 
             @Override
diff --git a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedStructureSetFrequencyOverridesTest.java b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedStructureSetFrequencyOverridesTest.java
index 2b8d9a68e..2c2e5c2ce 100644
--- a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedStructureSetFrequencyOverridesTest.java
+++ b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedStructureSetFrequencyOverridesTest.java
@@ -14,16 +14,18 @@ import net.minecraft.core.registries.Registries;
 import net.minecraft.resources.Identifier;
 import net.minecraft.resources.ResourceKey;
 import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.ChunkPos;
 import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.biome.BiomeResolver;
 import net.minecraft.world.level.biome.BiomeSource;
 import net.minecraft.world.level.biome.Climate;
 import net.minecraft.world.level.chunk.ChunkGeneratorStructureState;
 import net.minecraft.world.level.levelgen.RandomState;
 import net.minecraft.world.level.levelgen.structure.StructureSet;
+import net.minecraft.world.level.levelgen.structure.placement.AbstractSpreadingStructurePlacement;
 import net.minecraft.world.level.levelgen.structure.placement.RandomSpreadStructurePlacement;
 import net.minecraft.world.level.levelgen.structure.placement.RandomSpreadType;
 import net.minecraft.world.level.levelgen.structure.placement.StructurePlacement;
-import net.minecraft.world.level.levelgen.structure.placement.StructurePlacementType;
 import org.junit.BeforeClass;
 import org.junit.Test;
 
@@ -166,10 +168,10 @@ public class ModdedStructureSetFrequencyOverridesTest {
     ) {
         return new RandomSpreadStructurePlacement(
                 Vec3i.ZERO,
-                StructurePlacement.FrequencyReductionMethod.DEFAULT,
+                AbstractSpreadingStructurePlacement.FrequencyReductionMethod.DEFAULT,
                 1F,
                 salt,
-                Optional.of(new StructurePlacement.ExclusionZone(exclusionTarget, 1)),
+                Optional.of(new AbstractSpreadingStructurePlacement.ExclusionZone(exclusionTarget, 1)),
                 spacing,
                 separation,
                 RandomSpreadType.LINEAR);
@@ -183,6 +185,7 @@ public class ModdedStructureSetFrequencyOverridesTest {
                         RandomState.class,
                         BiomeSource.class,
                         long.class,
+                        ChunkPos.class,
                         long.class,
                         List.class);
         constructor.setAccessible(true);
@@ -190,6 +193,7 @@ public class ModdedStructureSetFrequencyOverridesTest {
                 null,
                 new EmptyBiomeSource(),
                 1L,
+                ChunkPos.ZERO,
                 1L,
                 sets);
     }
@@ -211,8 +215,8 @@ public class ModdedStructureSetFrequencyOverridesTest {
 
     private static final class EmptyBiomeSource extends BiomeSource {
         @Override
-        public Holder<Biome> getNoiseBiome(int x, int y, int z, Climate.Sampler sampler) {
-            return null;
+        public BiomeResolver createResolver(Climate.Sampler sampler) {
+            return (x, y, z) -> null;
         }
 
         @Override
@@ -226,18 +230,14 @@ public class ModdedStructureSetFrequencyOverridesTest {
         }
     }
 
-    private static final class UnsupportedPlacement extends StructurePlacement {
-        private UnsupportedPlacement() {
-            super(Vec3i.ZERO, FrequencyReductionMethod.DEFAULT, 1F, 1, Optional.empty());
-        }
-
+    private static final class UnsupportedPlacement implements StructurePlacement {
         @Override
-        protected boolean isPlacementChunk(ChunkGeneratorStructureState state, int x, int z) {
+        public boolean isStructureChunk(ChunkGeneratorStructureState state, int x, int z) {
             return false;
         }
 
         @Override
-        public StructurePlacementType<?> type() {
+        public com.mojang.serialization.MapCodec<? extends StructurePlacement> codec() {
             return null;
         }
     }
diff --git a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedTileParityTest.java b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedTileParityTest.java
index d87c20d51..e19701f43 100644
--- a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedTileParityTest.java
+++ b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedTileParityTest.java
@@ -19,6 +19,7 @@ import net.minecraft.world.level.block.Blocks;
 import net.minecraft.world.level.block.entity.BarrelBlockEntity;
 import net.minecraft.world.level.block.entity.ChestBlockEntity;
 import net.minecraft.world.level.block.entity.SignBlockEntity;
+import net.minecraft.world.level.block.entity.SignTextSlot;
 import net.minecraft.world.level.block.entity.SpawnerBlockEntity;
 import net.minecraft.world.level.storage.TagValueInput;
 import org.junit.BeforeClass;
@@ -61,9 +62,9 @@ public class ModdedTileParityTest {
 
         sign.loadWithComponents(TagValueInput.create(ProblemReporter.DISCARDING, registries, tile.nativeData().payload()));
 
-        assertEquals("Iris", sign.getFrontText().getMessage(0, false).getString());
-        assertEquals("parity", sign.getBackText().getMessage(3, false).getString());
-        assertEquals(DyeColor.BLUE, sign.getFrontText().getColor());
+        assertEquals("Iris", sign.getText(SignTextSlot.FRONT).getMessages(false).get(0).getString());
+        assertEquals("parity", sign.getText(SignTextSlot.BACK).getMessages(false).get(3).getString());
+        assertEquals(DyeColor.BLUE, sign.getText(SignTextSlot.FRONT).getColor());
     }
 
     @Test
diff --git a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedWaterEntitySpawnTest.java b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedWaterEntitySpawnTest.java
index 52ca89a7a..8578a381c 100644
--- a/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedWaterEntitySpawnTest.java
+++ b/adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedWaterEntitySpawnTest.java
@@ -12,8 +12,11 @@ import art.arcane.volmlib.util.math.RNG;
 import net.minecraft.SharedConstants;
 import net.minecraft.core.BlockPos;
 import net.minecraft.core.registries.BuiltInRegistries;
+import net.minecraft.core.registries.Registries;
 import net.minecraft.server.Bootstrap;
 import net.minecraft.server.level.ServerLevel;
+import net.minecraft.tags.BlockTags;
+import net.minecraft.tags.TagLoader;
 import net.minecraft.world.level.block.Block;
 import net.minecraft.world.level.block.Blocks;
 import net.minecraft.world.level.block.state.BlockState;
@@ -22,6 +25,8 @@ import org.junit.BeforeClass;
 import org.junit.Test;
 
 import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
 import java.util.Set;
 
 import static org.junit.Assert.assertEquals;
@@ -42,6 +47,8 @@ public class ModdedWaterEntitySpawnTest {
                 state.initCache();
             }
         }
+        BuiltInRegistries.BLOCK.prepareTagReload(new TagLoader.LoadResult<>(Registries.BLOCK, Map.of(
+                BlockTags.BLOCKS_MOTION, List.of(Blocks.OAK_FENCE.builtInRegistryHolder())))).apply();
     }
 
     @Test
diff --git a/adapters/modded-common/src/test/java/art/arcane/volmlib/nativelib/minecraft26_2/modded/NativeStructureOperationsTest.java b/adapters/modded-common/src/test/java/art/arcane/volmlib/nativelib/minecraft26_2/modded/NativeStructureOperationsTest.java
index 00c4436c6..43a5f6712 100644
--- a/adapters/modded-common/src/test/java/art/arcane/volmlib/nativelib/minecraft26_2/modded/NativeStructureOperationsTest.java
+++ b/adapters/modded-common/src/test/java/art/arcane/volmlib/nativelib/minecraft26_2/modded/NativeStructureOperationsTest.java
@@ -6,7 +6,11 @@ import art.arcane.volmlib.nativelib.minecraft26_2.modded.ModdedPlatformWorld;
 
 import net.minecraft.SharedConstants;
 import net.minecraft.server.Bootstrap;
-import net.minecraft.world.level.levelgen.feature.Feature;
+import net.minecraft.world.level.levelgen.feature.FallenTreeFeature;
+import net.minecraft.world.level.levelgen.feature.HugeBrownMushroomFeature;
+import net.minecraft.world.level.levelgen.feature.HugeRedMushroomFeature;
+import net.minecraft.world.level.levelgen.feature.OreFeature;
+import net.minecraft.world.level.levelgen.feature.TreeFeature;
 import net.minecraft.world.level.levelgen.structure.BoundingBox;
 import org.junit.BeforeClass;
 import org.junit.Test;
@@ -32,11 +36,11 @@ public class NativeStructureOperationsTest {
 
     @Test
     public void objectFeaturesMatchPaperGroups() {
-        assertEquals("trees", NativeStructureOperations.classifyFeature(Feature.TREE));
-        assertEquals("fallen_trees", NativeStructureOperations.classifyFeature(Feature.FALLEN_TREE));
-        assertEquals("mushrooms", NativeStructureOperations.classifyFeature(Feature.HUGE_BROWN_MUSHROOM));
-        assertEquals("mushrooms", NativeStructureOperations.classifyFeature(Feature.HUGE_RED_MUSHROOM));
-        assertNull(NativeStructureOperations.classifyFeature(Feature.ORE));
+        assertEquals("trees", NativeStructureOperations.classifyFeature(mock(TreeFeature.class)));
+        assertEquals("fallen_trees", NativeStructureOperations.classifyFeature(mock(FallenTreeFeature.class)));
+        assertEquals("mushrooms", NativeStructureOperations.classifyFeature(mock(HugeBrownMushroomFeature.class)));
+        assertEquals("mushrooms", NativeStructureOperations.classifyFeature(mock(HugeRedMushroomFeature.class)));
+        assertNull(NativeStructureOperations.classifyFeature(mock(OreFeature.class)));
     }
 
     @Test