The Revenant

In folklore, a ghost or walking corpse that is believed to have been reborn from death to haunt the living. Such creatures are part of the legends of various cultures, including Ancient Irish Celtic and Scandinavian mythology, and the stories of alleged visits of the Avengers were documented by English historians in the Middle Ages. The term "revenant" has been used interchangeably with "vampire" or "ghost" by folklorists, so it is sometimes considered to be a generic term for the undead.

People (spirits) themselves decide to return to their former flesh in order to somehow mess up, or take revenge on the living. They moved into their own buried body when it had already begun to decompose, but had not yet decomposed beyond recognition. Pieces of flesh were missing from this body, often exposing bones and internal organs, the skin hung in rags, and grave worms and their larvae swarmed in all the voids. There was a strong smell of rot. Could be missing limbs, etc. They drink the blood of their victims, but it is not known for what.