Spread the DPS across the stairs. When you do the pull, move them within melee range by pressing forward. Tank and spank him, with some tank and AOE healing here and there as needed. When you become a skeleton, click taunt on the tank only, use the 3 key for your bone shield, then spam 1 for melee and 4 for life drain. Use life drain every cooldown and reshield whenever it's down. When he places a puddle under the team, just press forward again, turn them, then continue. That's the whole fight. It's really easy once you learn it.

You may also want to place a nature resist totem down before the pull, and think about using shadow protection buff (if you have it) or the aura.