Don't use any heroes that have a clone or extra hero either, eg. Pixie, Dungeon Man or Skele. He consumes them for health. Wee witch, Shaman, and Thief do large amounts of magic damage and are really good against him, even ninja. Plant helps to negate the damage he does once below 50% health (and deals magic damage). Bone helps to stop him possessing one of your toons. And this probably won't help you now but void seems to have been made as a spectral counter.