there are four different sub-classes.
1.skeliton:these are the main and elite infantry for the undead the are just simply a persons skeliton and are smarter than zombies.
2.zombie:are the grunts of the undead they are weaker and dumber than skelitons and have decaying skin and some bones showing.
3.necromancers:are not undead but are mages that can raise the dead.usally clothed in black robes with a skull on it they are humans.
4.dead or turned necromancers that are far more powerful than normal ones are clothed in same robes buy have green skin and red eyes.
(note that the undead gain ranks by dead people if someon dies they can be brought back but if something undead dies then they are gone for good.all races can become undead.)