Custom Mob Crashes Minecraft instantly when spawned

I have created a new mod that is based on the game AOE III so I went a created a mob to add to my mod and started a test run. When I spawned the mob, it instantly crashed the game. This is very strange to me because I have other mobs in my mod that work just fine! It happens so randomly even when at first, the mob was okay but all of a sudden gets it! The whole point of the mod is to raise an army of these mobs and fight each other so i need to get it fixed right away. I am using Mcreator version 1.7.3 for Minecraft 1.7.10. If there is anyone who knows about this PLEASE HELP SOS.