Make it do the slime things

src/main/java/click/vpzom/coloredslime/mixin/PistonBlockEntityMixin.java

@@ -5,9 +5,7 @@ import net.minecraft.block.SlimeBlock;
 import net.minecraft.block.entity.PistonBlockEntity;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.Shadow;
-import org.spongepowered.asm.mixin.gen.Invoker;
 import org.spongepowered.asm.mixin.injection.At;
-import org.spongepowered.asm.mixin.injection.Inject;
 import org.spongepowered.asm.mixin.injection.ModifyVariable;
 
 @Mixin(PistonBlockEntity.class)
@@ -20,7 +18,7 @@ public class PistonBlockEntityMixin {
 	@Shadow
 	private BlockState pushedBlock;
 
-	@ModifyVariable(at = @At(value = "INVOKE", target = "Ljava/util/List;size()I"), method = "method_11503(F)V")
+	@ModifyVariable(at = @At(value = "INVOKE", target = "Ljava/util/List;size()I", ordinal = 0), method = "method_11503(F)V", allow = 1)
 	private boolean isSlime(boolean _ignored) {
 		return pushedBlock.getBlock() instanceof SlimeBlock;
 	}

src/main/java/click/vpzom/coloredslime/mixin/PistonHandlerMixin.java

@@ -0,0 +1,42 @@
+package click.vpzom.coloredslime.mixin;
+
+import net.minecraft.block.Block;
+import net.minecraft.block.BlockState;
+import net.minecraft.block.Blocks;
+import net.minecraft.block.SlimeBlock;
+import net.minecraft.block.piston.PistonHandler;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.world.World;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.gen.Invoker;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.Redirect;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+import org.spongepowered.asm.mixin.injection.callback.LocalCapture;
+
+@Mixin(PistonHandler.class)
+public abstract class PistonHandlerMixin {
+	@Shadow
+	private World world;
+
+	@Invoker
+	protected abstract boolean callMethod_11538(BlockPos pos);
+
+	@Inject(at = @At(value = "INVOKE", target = "Lnet/minecraft/block/BlockState;getBlock()Lnet/minecraft/block/Block;"), method = "calculatePush()Z", allow = 1, locals = LocalCapture.CAPTURE_FAILEXCEPTION)
+	private void calculatePushSlime(CallbackInfoReturnable<Boolean> info, int _i, BlockPos pos) {
+		if(world.getBlockState(pos).getBlock() instanceof SlimeBlock && !callMethod_11538(pos)) {
+			info.setReturnValue(false);
+		}
+	}
+
+	@Redirect(at = @At(value = "INVOKE", target = "Lnet/minecraft/block/BlockState;getBlock()Lnet/minecraft/block/Block;"), method = "tryMove(Lnet/minecraft/util/math/BlockPos;Lnet/minecraft/util/math/Direction;)Z")
+	private Block hackSlimeBlock(BlockState state) {
+		Block block = state.getBlock();
+		if(block instanceof SlimeBlock) {
+			return Blocks.SLIME_BLOCK;
+		}
+		return block;
+	}
+}

src/main/resources/coloredslime.mixins.json

@@ -2,7 +2,7 @@
 	"required": true,
 	"package": "click.vpzom.coloredslime.mixin",
 	"compatibilityLevel": "JAVA_8",
-	"mixins": ["SlimeBlockMixin", "BlockSettingsSounds", "PistonBlockEntityMixin"],
+	"mixins": ["SlimeBlockMixin", "BlockSettingsSounds", "PistonBlockEntityMixin", "PistonHandlerMixin"],
 	"injectors": {
 		"defaultRequire": 1
 	}