Revenants, taken from the Latin meaning "returning" or "come back", are fairly old and complex undead due to being somewhere between a vampire and a zombie. Despite being undead, revenants can still have all of their flesh, be nothing but bones, or anywhere in between. Another feature of the revenant is that when they finally confront their wrongdoer, their eyes will glow as they fixate on their culprit.
Those who return from the dead are wrongdoers in their lifetime, often described as wicked or vain or unbelievers. Often the revenants are associated with the spreading of disease among the living. The appropriate response is usually exhumation, followed by some form of decapitation, and burning or removal of the heart.
Originating in Western Europe, particularly England and Ireland, revenants were far more deadly than most monsters that traverse across the globe. Unlike the common undead, revenants had only one purpose in existence and that is vengeance. Whether murdered or wronged before death, these creatures terrorized the living until the wrong doer was found and is swiftly eliminated. They are widely regarded as strong, fast, and incredibly deadly but intelligent killing machines. While they are undead with one focus and that is revenge, they hold no special love or mercy to humans that are innocent and did not do them any wrong in their past life.
Two of the most terrifying factors of a revenant is their strength and speed. When a revenant is created, their strength and speed increases to immense levels, making them very formidable opponents in battle. Revenants would even retain all their memories that they had in their past life, making them all the more intelligent and cunning in the process. Their skills from past battles would be highly improved as well due to the mystical power coursing through their bodies and empowering them upon resurrection. Speaking of which, unlike other undead that were brought back with a mock soul, revenants were returned to the land of living with the same soul that departed from the body.
Revenants were also vampiric in nature. In the book of William of Newburgh called The Historia Rerum Angelicarum, it is said that the corpse of one revenant is reported to have been found in the grave, swollen and "suffused with blood". When it was pierced, a stream of blood flew out of the wound. This part of the story is paralleled in many accounts of alleged vampires, and the phenomenon it depicts is, in fact, known to occur frequently as part of the natural process of corpse decomposition.