Rakshashaar
Pretended to be Sir Isteval and met Cimien Wit while he was partying around.
While he was disguised as Sir Isteval he told us that the Rakshashaar had kidnapped his friend, Nadir who was some sort of Cleric and was controlled by a Rakshashaar to try and lure Sir Isteval to him.
Then he was defeated by Sir Isteeval (and friends? And then they closed a hell portal) which is likely part of the lie.
Nadir or the Endless Nadir has something to do with Yvain
We'll have to kill him on the material plane, and again in hell when his body reforms. No idea how we do that.