I have seen this creature you call "Calefactus" many times in my field studies. By all accounts, it appears to be a nigh-invulnerable core hound made from Fel energies. However, if what you say is true, and the Twilight's Hammer were planning to enslave it, then there may be a way to subdue the beast. The Shadowsworn, to the south-east, are known to perform dark rituals, including the enslavement of Fel creatures. Perhaps members of their order carry a clue to weakening Calefactus?