Revenants are one of several forms of Uroboros created on Sejm Island. When exposed to the virus, the cells are repaired and begin mutating. With the human brain dead, the emerging organism instead grows a fleshy "core" elsewhere on the body, which takes over brain functions. Consequently, destruction of the core will kill such a creature.
Created as research specimens, Revenants were the result of various human body parts being stitched together. The ability of the emerging organism to control the limbs would have given valuable insight into the organism's capabilities.[excerpt 1]