In many accounts the Souleaters are described as an undefinable force or collective consciousness that exists beyond the boundaries of most vampires’ perception. They are called mind-searing monstrosities, and it is said they can take many forms and manipulate many pawns.
According to these sources, members of other sects may well be under the sway of the Souleaters, as might any number of other denizens of the night. Werewolves, mortal mages, and the occasional inchoate nightmare-creature that finds its way into the world might be in league with these dark powers, knowingly or, more likely, completely obliviously. This secret war against the Souleaters is known as the Shadow Crusade among the devoted of the Tal’Mahe’Ra.
Classic World of Darkness lore says the Souleater is a fragment of a spiritual entity (most likely a Bane from the brood of the Eater-of-Souls). The Souleaters are native to the Deep Umbra, and some sources even claim that Vicissitude and Sanguinus were in fact parasitic diseases that originated in the Umbra and were brought to the physical realm by a Tzimisce named Andeleon.
This theory suggests that, just like a disease, those disciplines eat away at the body, mind, and soul of the infected individuals until they are consumed and overtaken by it, becoming Souleaters themselves. Supposedly, the Old Clan Tzimisce were the only Fiends able to isolate themselves and avoid becoming infected by Vicissitude. The True Black Hand was devoted to wipe out this alien invasion, while at the same time kept it a secret from the rest of the world.
The Souleaters can take over any creature, including Lupines, mages, vampires and mortals so long as the victim has become infected by them.
Fleshy Collectives - these creatures are basically huge blobs of oozing free-floating flesh and guts which squish about, absorbing others into them. The victims' brains continue to float about inside the thing, and they remain conscious and in extreme suffering, though not in control of their actions.
Ghastly Babies - these creatures resemble human infants. Their bodies and proportions are nearly the same, but those who glimpse their faces know the truth of their horrifying existence - they are Souleaters who crawled from their host before their hosts fully developed. In most cases, their host was killed before they finished taking it over. They are incapable of changing form and must consume flesh in order to continue their development (which usually leaves a bloody trail of chopped-up half-consumed bodies).
Shamblers - creatures that resembles humans with melting skin.
- The concept of Vicissitude as an infectious disease connected to the Souleaters of the Deep Umbra seems to be abandoned by game developers in later editions of the game. V20 revives the concept as the Asakku.