I ascended my Monk/Ele a couple of hours earlier and here's what I used (pure Monk):
Blessed Aura
Divine Boon
Healing Breeze
That's it. I cast all three before the cut scene. Then after the cut scene ended, C + Space to attack. Run up close so the dopple won't use the bow but the melee weapon. Spam Healing Breeze as often as you can and keep attacking the dopple (I'd cast HB as soon as I had enough energy again). It's probably not the fastest way to kill him/her, but it worked and that's all that matters.
