I tried blood furnace, but failed at that big head guy on the gauntlet type bit before it. My mana just didn't last out. I was nuking them fine, but when it got to the last group...there was no mana left. I swapped in my paladin (80) and done that boss with him. I then swapped my shaman back in for the rest of the instance....surprisingly, they allgot the achievement....thought it would've been for doing all the bosses.