to xfa:
kill everything in the room first
Pull the boss and run around the room around the pillars with the boss chasing you. Don't stop running and hit the boss only with dots and instant cast skills, no long casting.
every now and then the boss will stop to spin on hymself, us that time to heal urself.
Also don't look at the boss while running, look forward and us your minimap to know where the boss is.
Basically its kitting the boss around the room