Made it so placed mimic blocks replace the block that you place it on unless you hold shift. Also worked on dungeon schematic saving/loading.

src/main/java/WayofTime/bloodmagic/entity/mob/EntityMimic.java

@@ -0,0 +1,247 @@
+package WayofTime.bloodmagic.entity.mob;
+
+import net.minecraft.block.Block;
+import net.minecraft.entity.EntityLivingBase;
+import net.minecraft.entity.EnumCreatureAttribute;
+import net.minecraft.entity.SharedMonsterAttributes;
+import net.minecraft.entity.ai.EntityAIAttackMelee;
+import net.minecraft.entity.ai.EntityAIHurtByTarget;
+import net.minecraft.entity.ai.EntityAILeapAtTarget;
+import net.minecraft.entity.ai.EntityAILookIdle;
+import net.minecraft.entity.ai.EntityAINearestAttackableTarget;
+import net.minecraft.entity.ai.EntityAISwimming;
+import net.minecraft.entity.ai.EntityAIWander;
+import net.minecraft.entity.ai.EntityAIWatchClosest;
+import net.minecraft.entity.monster.EntityIronGolem;
+import net.minecraft.entity.monster.EntityMob;
+import net.minecraft.entity.player.EntityPlayer;
+import net.minecraft.init.Blocks;
+import net.minecraft.init.MobEffects;
+import net.minecraft.init.SoundEvents;
+import net.minecraft.item.ItemStack;
+import net.minecraft.network.datasync.DataParameter;
+import net.minecraft.network.datasync.DataSerializers;
+import net.minecraft.network.datasync.EntityDataManager;
+import net.minecraft.pathfinding.PathNavigate;
+import net.minecraft.pathfinding.PathNavigateClimber;
+import net.minecraft.potion.PotionEffect;
+import net.minecraft.util.SoundEvent;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.world.World;
+
+public class EntityMimic extends EntityMob
+{
+    /**
+     * Copy of EntitySpider's AI (should be pretty evident...)
+     */
+    private static final DataParameter<Byte> CLIMBING = EntityDataManager.<Byte>createKey(EntityMimic.class, DataSerializers.BYTE);
+
+    public EntityMimic(World worldIn)
+    {
+        super(worldIn);
+        this.setSize(1.4F, 0.9F);
+    }
+
+    public ItemStack getItemStack()
+    {
+        return new ItemStack(Blocks.CHEST);
+    }
+
+    protected void initEntityAI()
+    {
+        this.tasks.addTask(1, new EntityAISwimming(this));
+        this.tasks.addTask(3, new EntityAILeapAtTarget(this, 0.4F));
+        this.tasks.addTask(4, new EntityMimic.AISpiderAttack(this));
+        this.tasks.addTask(5, new EntityAIWander(this, 0.8D));
+        this.tasks.addTask(6, new EntityAIWatchClosest(this, EntityPlayer.class, 8.0F));
+        this.tasks.addTask(6, new EntityAILookIdle(this));
+        this.targetTasks.addTask(1, new EntityAIHurtByTarget(this, false, new Class[0]));
+        this.targetTasks.addTask(2, new EntityMimic.AISpiderTarget(this, EntityPlayer.class));
+        this.targetTasks.addTask(3, new EntityMimic.AISpiderTarget(this, EntityIronGolem.class));
+    }
+
+    /**
+     * Returns the Y offset from the entity's position for any entity riding
+     * this one.
+     */
+    @Override
+    public double getMountedYOffset()
+    {
+        return (double) (this.height * 0.5F);
+    }
+
+    /**
+     * Returns new PathNavigateGround instance
+     */
+    @Override
+    protected PathNavigate getNewNavigator(World worldIn)
+    {
+        return new PathNavigateClimber(this, worldIn);
+    }
+
+    @Override
+    protected void entityInit()
+    {
+        super.entityInit();
+        this.dataManager.register(CLIMBING, Byte.valueOf((byte) 0));
+    }
+
+    /**
+     * Called to update the entity's position/logic.
+     */
+    @Override
+    public void onUpdate()
+    {
+        super.onUpdate();
+
+        if (!this.worldObj.isRemote)
+        {
+            this.setBesideClimbableBlock(this.isCollidedHorizontally);
+        }
+    }
+
+    @Override
+    protected void applyEntityAttributes()
+    {
+        super.applyEntityAttributes();
+        this.getEntityAttribute(SharedMonsterAttributes.MAX_HEALTH).setBaseValue(16.0D);
+        this.getEntityAttribute(SharedMonsterAttributes.MOVEMENT_SPEED).setBaseValue(0.3D);
+    }
+
+    @Override
+    protected SoundEvent getAmbientSound()
+    {
+        return SoundEvents.ENTITY_SPIDER_AMBIENT;
+    }
+
+    @Override
+    protected SoundEvent getHurtSound()
+    {
+        return SoundEvents.ENTITY_SPIDER_HURT;
+    }
+
+    @Override
+    protected SoundEvent getDeathSound()
+    {
+        return SoundEvents.ENTITY_SPIDER_DEATH;
+    }
+
+    @Override
+    protected void playStepSound(BlockPos pos, Block blockIn)
+    {
+        this.playSound(SoundEvents.ENTITY_SPIDER_STEP, 0.15F, 1.0F);
+    }
+
+    /**
+     * returns true if this entity is by a ladder, false otherwise
+     */
+    @Override
+    public boolean isOnLadder()
+    {
+        return this.isBesideClimbableBlock();
+    }
+
+    /**
+     * Sets the Entity inside a web block.
+     */
+    @Override
+    public void setInWeb()
+    {
+
+    }
+
+    /**
+     * Get this Entity's EnumCreatureAttribute
+     */
+    @Override
+    public EnumCreatureAttribute getCreatureAttribute()
+    {
+        return EnumCreatureAttribute.ARTHROPOD;
+    }
+
+    @Override
+    public boolean isPotionApplicable(PotionEffect potioneffectIn)
+    {
+        return potioneffectIn.getPotion() == MobEffects.POISON ? false : super.isPotionApplicable(potioneffectIn);
+    }
+
+    /**
+     * Returns true if the WatchableObject (Byte) is 0x01 otherwise returns
+     * false. The WatchableObject is updated using setBesideClimableBlock.
+     */
+    public boolean isBesideClimbableBlock()
+    {
+        return (((Byte) this.dataManager.get(CLIMBING)).byteValue() & 1) != 0;
+    }
+
+    /**
+     * Updates the WatchableObject (Byte) created in entityInit(), setting it to
+     * 0x01 if par1 is true or 0x00 if it is false.
+     */
+    public void setBesideClimbableBlock(boolean climbing)
+    {
+        byte b0 = ((Byte) this.dataManager.get(CLIMBING)).byteValue();
+
+        if (climbing)
+        {
+            b0 = (byte) (b0 | 1);
+        } else
+        {
+            b0 = (byte) (b0 & -2);
+        }
+
+        this.dataManager.set(CLIMBING, Byte.valueOf(b0));
+    }
+
+    public float getEyeHeight()
+    {
+        return 0.65F;
+    }
+
+    static class AISpiderAttack extends EntityAIAttackMelee
+    {
+        public AISpiderAttack(EntityMimic spider)
+        {
+            super(spider, 1.0D, true);
+        }
+
+        /**
+         * Returns whether an in-progress EntityAIBase should continue executing
+         */
+        public boolean continueExecuting()
+        {
+            float f = this.attacker.getBrightness(1.0F);
+
+            if (f >= 0.5F && this.attacker.getRNG().nextInt(100) == 0)
+            {
+                this.attacker.setAttackTarget((EntityLivingBase) null);
+                return false;
+            } else
+            {
+                return super.continueExecuting();
+            }
+        }
+
+        protected double getAttackReachSqr(EntityLivingBase attackTarget)
+        {
+            return (double) (4.0F + attackTarget.width);
+        }
+    }
+
+    static class AISpiderTarget<T extends EntityLivingBase> extends EntityAINearestAttackableTarget<T>
+    {
+        public AISpiderTarget(EntityMimic spider, Class<T> classTarget)
+        {
+            super(spider, classTarget, true);
+        }
+
+        /**
+         * Returns whether the EntityAIBase should begin execution.
+         */
+        public boolean shouldExecute()
+        {
+            float f = this.taskOwner.getBrightness(1.0F);
+            return f >= 0.5F ? false : super.shouldExecute();
+        }
+    }
+}