I have some ideas.

why not let the zombies have a slash attack that just deals damage, and are the zombies going to be just human what about a ogre zombie or maybe even a dragon zombie?

how about a zombie that some crazy insane wizard/sorcerer decided to graft a wand of fireball on a zombie that used to be a super smart person in life and knows enough how to adtivate it. any of these doing anything for ya?