In my mod, there's a block that when right clicked spawns the Monkeysaur entity:

package tlhpoe.fs.block;

import net.minecraft.block.Block;
import net.minecraft.block.material.Material;
import net.minecraft.client.renderer.texture.IIconRegister;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.init.Blocks;
import net.minecraft.util.IIcon;
import net.minecraft.world.World;
import tlhpoe.fs.entity.boss.EntityMonkeysaur;
import cpw.mods.fml.relauncher.Side;
import cpw.mods.fml.relauncher.SideOnly;

public class BlockMonkeysaurAltar extends Block {
public IIcon iSide, iTop;

public BlockMonkeysaurAltar() {
	super(Material.rock);
}

@Override
@SideOnly(Side.CLIENT)
public IIcon getIcon(int side, int p_149691_2_) {
	if(side == 1)
		return iTop;
	return iSide;
}

@Override
@SideOnly(Side.CLIENT)
public void registerBlockIcons(IIconRegister p_149651_1_) {
	this.iSide = Blocks.gold_block.getBlockTextureFromSide(0);
	this.iTop = p_149651_1_.registerIcon("fs:monkeysaurAltar");
	this.blockIcon = this.iTop;
}

@Override
public boolean onBlockActivated(World w, int x, int y, int z, EntityPlayer p_149727_5_, int p_149727_6_, float p_149727_7_, float p_149727_8_, float p_149727_9_) {
	if(!w.isRemote) {
		EntityMonkeysaur e = new EntityMonkeysaur(w);
		e.posX = x;
		e.posY = y;
		e.posZ = z;
		w.spawnEntityInWorld(e);
		w.setBlock(x, y, z, Blocks.air);
	}
	return true;
}
}

 

The problem is, the entity appears and I can't interact with it and it doesn't do anything. A few seconds later it disappears.

 

Here's the entity's code:

package tlhpoe.fs.entity.boss;

import net.minecraft.command.IEntitySelector;
import net.minecraft.entity.Entity;
import net.minecraft.entity.EntityLivingBase;
import net.minecraft.entity.SharedMonsterAttributes;
import net.minecraft.entity.ai.EntityAIAttackOnCollide;
import net.minecraft.entity.ai.EntityAIHurtByTarget;
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.boss.IBossDisplayData;
import net.minecraft.entity.monster.EntityMob;
import net.minecraft.entity.monster.IMob;
import net.minecraft.world.World;

public class EntityMonkeysaur extends EntityMob implements IBossDisplayData, IMob {
private static final IEntitySelector attackEntitySelector = new IEntitySelector() {
	public boolean isEntityApplicable(Entity par1Entity) {
		return par1Entity instanceof EntityLivingBase && !(par1Entity instanceof EntityMonkeysaur);
	}
};

public EntityMonkeysaur(World par1World) {
	super(par1World);
	this.setSize(0.6F * 4, 1.8F * 4);
	this.tasks.addTask(0, new EntityAISwimming(this));
	this.tasks.addTask(1, new EntityAIAttackOnCollide(this, EntityLivingBase.class, 1.0D, false));
	this.tasks.addTask(7, new EntityAIWander(this, 1.0D));
	this.tasks.addTask(8, new EntityAIWatchClosest(this, EntityLivingBase.class, 8.0F));
	this.tasks.addTask(8, new EntityAILookIdle(this));
	this.targetTasks.addTask(1, new EntityAIHurtByTarget(this, true));
	this.targetTasks.addTask(2, new EntityAINearestAttackableTarget(this, EntityLivingBase.class, 0, false, false, attackEntitySelector));
	this.experienceValue = 350;
}

@Override
protected void applyEntityAttributes() {
	super.applyEntityAttributes();
	this.getEntityAttribute(SharedMonsterAttributes.followRange).setBaseValue(64.0D);
	this.getEntityAttribute(SharedMonsterAttributes.maxHealth).setBaseValue(200.0D);
	this.getEntityAttribute(SharedMonsterAttributes.attackDamage).setBaseValue(10);
	this.getEntityAttribute(SharedMonsterAttributes.movementSpeed).setBaseValue(0.23000000417232513D);
}

@Override
public void setInWeb() {
}

@Override
protected void despawnEntity() {
	this.entityAge = 0;
}

@Override
protected void fall(float par1) {
}

@Override
protected boolean isAIEnabled() {
	return true;
}
}

If I remember, when I created a mob, that I didn't want to despawn I made it:

 

@Override
protected void despawnEntity() {}

Doesn't fix that problem.

Wait wait wait.

 

How do you have this:

Blocks.air

 

Shouldn't it be Block.air?

Shouldn't you have also gotten an error?

 

Can I see where you registered your Entity, or anything that relates to that Entity?

I'm using 1.7.2, Minecraft stores its blocks in the Blocks class.

 

Here's where I do my entity registering:

package tlhpoe.fs.helper;

import net.minecraft.client.renderer.entity.Render;
import net.minecraft.entity.Entity;
import tlhpoe.fs.entity.EntityIceCreeper;
import tlhpoe.fs.entity.EntityWaterCreeper;
import tlhpoe.fs.entity.boss.EntityMonkeysaur;
import tlhpoe.fs.entity.render.RenderFSCreeper;
import tlhpoe.fs.entity.render.RenderMonkeysaur;
import cpw.mods.fml.client.registry.RenderingRegistry;
import cpw.mods.fml.common.registry.EntityRegistry;

public class EntityHelper {
public static void doServer() {
	doEntity(EntityIceCreeper.class, "iceCreeper", 0xFFFFFF, 0x00FFFF);
	doEntity(EntityWaterCreeper.class, "waterCreeper", 0x0F8FFF, 0x00B2FF);
	doEntity(EntityMonkeysaur.class, "monkeysaur", 0x663300, 0x472400);
}

public static void doClient() {
	doRender(EntityIceCreeper.class, new RenderFSCreeper("ice"));
	doRender(EntityWaterCreeper.class, new RenderFSCreeper("water"));
	doRender(EntityMonkeysaur.class, new RenderMonkeysaur());
}

private static void doEntity(Class<? extends Entity> clazz, String name, int bgColor, int spotColor) {
	int id = EntityRegistry.findGlobalUniqueEntityId();
	EntityRegistry.registerGlobalEntityID(clazz, name, id, bgColor, spotColor);
}

private static void doRender(Class<? extends Entity> clazz, Render render) {
	RenderingRegistry.registerEntityRenderingHandler(clazz, render);
}
}

 

I can spawn it just fine with the spawn egg.

Oh I thought you were using 1.6, my bad.

 

Hmm. Strange, as if its spawning a ghost entity.

 

Try looking at other onBlockActivated methods.

In BlockWorkbench, it activates when

 

(world.isRemote), try removing the !

If I remove the !, it spawns the entity client side and it just makes the game confused a little.

 

If I completely remove the if statement, same result.

Fixed it, didn't set the rotation angles.