The poison cloud strategy works using death cloud as well (AI, mind you). Death cloud has the advantage that you only have to cast it once, as the plague stays on the old monk until he's dead rather than dissipating after a bit. You don't even really need the Dragon Bone Smasher or Meat Cleaver or anything like that. If you get the Old Monk to follow you to one side of the room, then run to the other side (with the graverobber's ring on, mind you), you'll lose him. I find the right side of the room is the safer side to hide/cast from - fewer obstacles. After losing the monk, move to the right side far back (relative to the door you enter through), move close enough to cast death cloud, then move back and turn off your controller and wait for him to die :-)
(or don't turn off your controller - I've gotten a bit paranoid about leaving it on when I'm not actively doing stuff, after accidentally stabbing stockpile Thomas)
