Heroic mode: This boss is really hard. We had a solid group of Pally tank (me), pally healer, hunter, elemental shaman, and a warlock. We ran into the problem where we would kill him to fast and the pure energy would come out to fast and kill us. The method we  used to beat him was this: I tank him pally healing me very slow dps to 85%, stop dps, warlock takes down pure energy, than goes to drain life. We had our elemental shaman healing the warlock. The hunter sat in back and was danceing or sleeping till 25% where we burned him down. This guy doesnt have much hp. You just have to take ur time.