I am attempting to create a sheep like mob but I keep getting this error - http://pastebin.com/qmEb75Mr
Here Is my code - http://pastebin.com/uz14e5Uj
Your problem is you are using the vanilla RenderEntitySheep class which expects an EntitySheep, but your mob extends EntityMob - it is NOT an EntitySheep, thus you get a class cast exception.
Create your own renderer and model, OR extend EntitySheep (and ModelSheep) and re-implement the mob logic (implement IMob, too, in your Entity class, if you go this route).
It's a tough choice to make, but the latter is probably the better choice if you want your entity to count as a sheep, and the first if you don't care about that.