The perfect Necropolis.

Zombie griffins are better than vampire griffins. And in general, I saw dead cyclops on some map in the fifth game. There's also a mod for the fifth part that adds rotting ents; all these creatures look quite appropriate in the game. Of course, if we're talking about the sixth part, there's no necromancy there; the undead only raise their own in order to maintain balance, so all of this is irrelevant to it, but that's boring.