Kezef The Chaos Hound
Kezef the Chaos Hound is a monstrous skeletal dog with maggots in place of flesh that consumes the souls of the faithful in the afterlife (those who focuses their worship on one god) who may have been created by Jergal. As the gods got anoid with being unable to claim their best followers, they chased it to Barrens of Doom and Despair (a plane that exist in the world Tree and World axis model), like the story of Fenerus, the gods challenged Kezef to break out of their chains made by Gond. Agreeing but only If he gets to bite someone's arm off if it does work, Tyr performs the same role as the norse version and sacrifices his arm. Kezef was chained and Mystra created a magic self-repairing vail to double insurance, with no dity or mortal being allowed to interact with him. Kept feed with some divine essence from the arm.
Has a grudge against Mask, which is a good thing because this drives it to spend more time hunting down Mask than eating souls.
In third edition Kezef is CR 21.