necromancy
Did you know immortals can revive the dead? There are generally three ways to do it. I will only cover the single way that was first implemented. The blood of a living organism poured into the mouth of a dead organism of the same type will restore life to the dead one, but will tie the revived one to the living one eternally.. This is dangerous unless the revived is released from its obligation or a release agreement reached/granted. Otherwise the difference between walking undead and zombie can be profound.