Vestige (Essence)

"It was fascinating to watch a vestige gradually absorbing Azure Plasm and converting it from the general to specific, so that over time it slowly took on the size and shape of a hulking, reptilian daedroth."

- Doctor Rythandius

Vestige - the essence of any Daedra, analog of the soul of mortals.

Soul Shriven
Each is a mortal kidnaped from Mundus at the moment of death, his or her soul stolen by Molag Bal, and given in exchange the vestige that enables him or her to form a counterfeit body in Coldharbour. But they are not native to Oblivion, so a Soul Shriven's body is a imitation of the body worn in life, suffering rapid wear and decay until it dies, for its vestige only forms a body once again, over and over, like a Daedra.