Undead

The undead are creatures that were previously alive but live no longer, yet are also not dead. In some cases, undead can be failed lifeforms that have some of the characteristics of life but fail in some critical ways to meet them all.
All undead can be divided into two camps: corporeal undead and incorporeal undead (usually called apparitions).

Corporeal Undead

Corporeal Undead, or just Undead, can trace their unnatural reanimation back to the Deadlands, the plane of death created where the Abyss and the Ethereal Plane intersect. Some such creatures draw energy directly from this plane, which is usually anathema to the living, whereas others were animated through magic that was scribed in the plane. The rest are undead afflicted with Abyssalism, which draws directly from the Abyss, or undead reanimated by a powerful spirit possessing its corpse. These are not necessarily mutually exclusive.
Types of corporeal undead include:

• Abyssalites, such as Wights and Revenants, that have been cursed by the Abyss
• Alluvians, slime-like masses animated by a shade
• Vatheks, Vetalas, and Jiangshi, all vessels reanimated by Kirin, Totems, or Demons, respectively
• Harbingers and Necrotars, vessels used by Djinn and Gods, respectively, as undead avatars
• Lasedons, undead that act on their own unless compelled to by someone else; includes Ghouls, Ghasts, Draugr, Mummies, and Demiliches
• Moroi, undead mogwai that harbor powerful anima-level spirits and possess intelligence and free will; includes Pharaohs, Banshees, and Liches
• Vampires, the closest to being alive of any undead, but need to feed on the living in order to survive; includes Incubi, Succubi, Vrykolakas, and Bodaks
• Yurei, similar to Moroi, but the spirits animating these mogwai are either tied to a Titan or are former divine beings
• Zombies, undead thralls that (usually) obey their creator, but lack much capacity for independence beyond what specific instructions they're endowed with; includes Dregs, Gigases, and Vexin

Apparitions

Apparitions are incorporeal entities that have no substance outside the Astral Plane or the Deadlands. They exist as masses of energy that only partially exist on the material plane, making them difficult to interact with unless using weapons or tools specifically designed to. While mostly considered undead, not all apparitions strictly are, though they all share their incorporeal nature and are generally disembodied.
Types of apparitions include:

• Demiurges, anima-level apparitions with powerful wills and generally strong magic; includes Strigois (vampire souls), Phantasms (lich souls), and Willowisps
• Ghosts, the disembodied souls of the dead who have not been able to pass on; includes Specters, Phantoms, Wisps, and Kadavers
• Suli, the degenerated essence of formerly higher beings, or a lower being empowered to such a degenerate state, and are not considered true undead; includes Idols (fallen gods) and Zabaniyya (fallen angels)