Okay, so I am onto the Stillshrine of Miriam, characters are all level 27. (Well, at least my main party.) I've decided I want to do the Ithuno/Deathbringer challenge. I have the Barheim key, and I know exactly where he spawns.

So, I'm up to about 40 restarts of the game because he never appears! Are there certain conditions that make him appear, or is it completely random? And if it's random, what's the % Chance of spawn?