There are three kinds of undeath in the world of Sigrogana.
The first is Cladis Mortem Null, which are mindless undead such as zombies. They're not sentient and often just rotting corpses powered by Focus alone, those undead only have the purpose of consuming the Focus of the living.
The second is Cladis Mortem, which are sentient undead such as Liches. Not a lot is known about this stage of the undead curse, only what it spawns.
The third is unliving, which are creatures that are not mortal but do not possess Cladis Mortem such as Vampires.