How to make a evoker type entity (I want to make a necromancer). How do I do this?

So I want to make a entity thats similar to an evoker, I want to make a necromancer. I need to figure out how to make zombies spawn in when you get to close to the necromancer.  I don't want the hand animation if it's to difficult. The necromancer is a biped (stands on two legs and two arms) if that matters. does anyone know how this is done? If so, please help me!