public class GemGuardianEntity extends Monster {
 
    public GemGuardianEntity(EntityType<? extends Monster> type, Level level) {
        super(type, level);
    }
 
    public static AttributeSupplier.Builder createAttributes() {
        return Monster.createMonsterAttributes()
                .add(Attributes.MAX_HEALTH, 30.0)
                .add(Attributes.ATTACK_DAMAGE, 6.0)
                .add(Attributes.MOVEMENT_SPEED, 0.25)
                .add(Attributes.FOLLOW_RANGE, 24.0);
    }
 
    @Override
    protected void registerGoals() {
        this.goalSelector.addGoal(0, new FloatGoal(this));
        this.goalSelector.addGoal(1, new MeleeAttackGoal(this, 1.2D, false));
        this.goalSelector.addGoal(2, new WaterAvoidingRandomStrollGoal(this, 1.0D));
        this.goalSelector.addGoal(3, new LookAtPlayerGoal(this, Player.class, 8.0f));
        this.goalSelector.addGoal(4, new RandomLookAroundGoal(this));
 
        this.targetSelector.addGoal(1, new NearestAttackableTargetGoal<>(this, Player.class, true));
    }
}

public static final DeferredRegister<EntityType<?>> ENTITY_TYPES =
        DeferredRegister.createEntities(MOD_ID);
 
public static final DeferredHolder<EntityType<?>, EntityType<GemGuardianEntity>> GEM_GUARDIAN =
        ENTITY_TYPES.registerEntityType("gem_guardian",
                GemGuardianEntity::new, MobCategory.MONSTER,
                builder -> builder
                        .sized(0.6f, 1.95f)
                        .clientTrackingRange(80));

public MasterCapstoneMod(IEventBus modEventBus, ModContainer container) {
    ENTITY_TYPES.register(modEventBus);
    modEventBus.addListener(MasterCapstoneMod::onEntityAttributes);
}
 
@SubscribeEvent
public static void onEntityAttributes(EntityAttributeCreationEvent event) {
    // ⚠️ Monster 상속 Entity는 반드시 여기에 등록해야 합니다.
    // 누락 시 /summon 에서 NullPointerException 발생.
    event.put(GEM_GUARDIAN.get(), GemGuardianEntity.createAttributes().build());
}

public class GemGuardianModel extends EntityModel<LivingEntityRenderState> {
 
    public static final ModelLayerLocation LAYER_LOCATION =
            new ModelLayerLocation(
                    Identifier.fromNamespaceAndPath("master_capstone", "gem_guardian"),
                    "main"
            );
 
    public static LayerDefinition createBodyLayer() {
        MeshDefinition mesh = new MeshDefinition();
        PartDefinition partDef = mesh.getRoot();
 
        partDef.addOrReplaceChild("head",
                CubeListBuilder.create().texOffs(0, 0)
                        .addBox(-4.0f, -8.0f, -4.0f, 8, 8, 8, new CubeDeformation(0.0f)),
                PartPose.offset(0.0f, 0.0f, 0.0f));
 
        partDef.addOrReplaceChild("body",
                CubeListBuilder.create().texOffs(16, 16)
                        .addBox(-4.0f, 0.0f, -2.0f, 8, 12, 4, new CubeDeformation(0.0f)),
                PartPose.offset(0.0f, 0.0f, 0.0f));
 
        // 오른팔, 왼팔, 오른다리, 왼다리 동일 구조로 추가
        // (GemGuardianModel.java 전체 코드 참고)
 
        return LayerDefinition.create(mesh, 64, 32);
    }
 
    @Override
    public void setupAnim(LivingEntityRenderState renderState) {
        this.head.yRot = renderState.yRot * Mth.DEG_TO_RAD;
        this.head.xRot = renderState.xRot * Mth.DEG_TO_RAD;
 
        float pos = renderState.walkAnimationPos;
        float speed = renderState.walkAnimationSpeed;
 
        this.rightArm.xRot = Mth.cos(pos * 0.6662f + Mth.PI) * 2.0f * speed * 0.5f;
        this.leftArm.xRot  = Mth.cos(pos * 0.6662f) * 2.0f * speed * 0.5f;
        this.rightLeg.xRot = Mth.cos(pos * 0.6662f) * 1.4f * speed;
        this.leftLeg.xRot  = Mth.cos(pos * 0.6662f + Mth.PI) * 1.4f * speed;
    }
}

public class GemGuardianRenderer
        extends MobRenderer<GemGuardianEntity, LivingEntityRenderState, GemGuardianModel> {
 
    private static final Identifier TEXTURE =
            Identifier.fromNamespaceAndPath("master_capstone",
                    "textures/entity/gem_guardian.png");
 
    public GemGuardianRenderer(EntityRendererProvider.Context ctx) {
        super(ctx, new GemGuardianModel(ctx.bakeLayer(GemGuardianModel.LAYER_LOCATION)), 0.5f);
    }
 
    @Override
    public LivingEntityRenderState createRenderState() {
        return new LivingEntityRenderState();
    }
 
    @Override
    public Identifier getTextureLocation(LivingEntityRenderState renderState) {
        return TEXTURE;
    }
}

@SubscribeEvent
public static void onRegisterRenderers(EntityRenderersEvent.RegisterRenderers event) {
    event.registerEntityRenderer(MasterCapstoneMod.GEM_GUARDIAN.get(),
            GemGuardianRenderer::new);
}
 
@SubscribeEvent
public static void onRegisterLayerDefinitions(EntityRenderersEvent.RegisterLayerDefinitions event) {
    event.registerLayerDefinition(GemGuardianModel.LAYER_LOCATION,
            GemGuardianModel::createBodyLayer);
}