Revenants are "spontaneous vampires", clanless examples of why the Kindred try not to kill when they feed.
Overview[]
While most individuals polluted by Vitae do not normally rise upon death, sufficiently low Humanity by their accidental sires dooms some of their deceased victims and ghouls to rise a few nights later as pseudo-Kindred lacking Blood Potency and without the ability to retain Vitae over the daysleep, sweating it out during their slumber. Needless to say, theirs is a miserable lot of constant fear of hunger frenzy and relatively easy possession by Strix, and they (and their creators) are usually killed to uphold the Masquerade.
There is a way to escape the horrible unlife of a revenant apart from Final Death, however; it is possible to Embrace them, at which point they become, for all intents and purposes, a normal, clanned childe of the sire who "adopted" them. Indeed, a cross-clan bloodline, the Neglatu, does not lose Humanity for adopting a revenant, so long as they initiate said childe into the bloodline in the process.