you need to kill his adds asap, one for each column, to weaken him.
grab the key at the backside of the room, and touch the
A Recall Obelisk
at ( -236, -149, -319 )
/waypoint -235.9, -149.49, -318.94
to teleport back to entry hall.
the trick here is to attack him until he ducks and prepares to leap. At this time you need to move behind one of the 4 smaller dragons. He will hit them and destroy them. Repeat until the healing he receives from them is lower than your dps, and take him down. If one of the gargoyles throws you while he is casting, this will not work.
fight him at the center stage, on a corner in order to be able to click an electrified pillar. Paste your back to the arch (KB!).
fight the statue until it begins to shimmer in either blue or red (near 50% of his life).
when you see the wording come on the screen, you need to click a pillar until the central stage gets lit by
an arch of electricity in the opposite color of his aura
.