Undead beings cannot heal afflictions unless they have Recuperation or Immortal, except through Gift of Health. Undead are immune to the instant death that accompanies certain afflictions, such as losing one's head. Undead do not need any supplies. Leaders with Death get +30 undead leadership, and those with Blood Magic get +5 undead leadership. The undead can still be diseased, but do not lose health or gain additional afflictions from it, they only spread it.
Undead Leaders have their maxage increased by 50% per point of Death magic. Undead Priests can reanimate undead. Nations that can reanimate the undead, such EA Lanka, MA Sceleria, and MA Ermor get the ability to have priests to reanimate the undead, and the Priests can lead 15 undead per holy level. A commander with a reanimation bonus apples that to the number of undead it raises by (such as the spell Reanimation) and/or the command Reanimate, these apply separately. Certain items can also increase the number undead raised.
Undead units are subject to banishment, as are demons. Undead and demon units require undead leadership, which is generally conferred by skill in Death magic (or being an undead commander). Zombies aren’t going to take orders from just anybody. That being said, Longdead will take orders from a leader with undead leadership. A squad that mixes undead and non-undead gets a -1 morale penalty. Units that are both undead and magic beings require undead leadership