Alright this is cake heres how.

Spread your team out so if he does puddle only one of them gets hit. I really never get hit by more then 1-2 puddles max really. Use 4X Healing Stream totems as this is not really a DPS race ever just slow and steady. Make sure if you use FTL setup, you have some way of your followers targetting him (/assist) and spam 3 and 4 on everyone but add 2 to your tank (thats taunt when you get turned into skellys).

Move out of the puddles and heal when needed but try and tank him facing away from your team then you won't get hit by his shadowbolt volley. This guy is probably the easiest boss in the instance once you figure him out. Save your bloodlust for near the end of his death and use it right after you turn back into human form.