Like everyone else that was helpful said, hide back in the safe room! Other wizards will spawn and disappear, just gotta keep killing the knights as they come in. If the shrieker spawns, do not panic. If you sit in the room before the shrieker room it will despawn. Eventually Xyor will start popping his head in. I killed him very slowly so in my experience he (she, it? who cares Xyor is a -blam!-in bitch) does not despawn; I always wanted confirmation that Xyor would not despawn before this strategy but could not find it. You got it bro! Best with an icebreaker, but if you do not have it bring some weapon packs, crack open a cold one, light that J, and cheese him out.