Approx 4 million HP
It takes about 2 million to get him to the 50% mark where he goes up the hill.
Then he usually reactivates with about 100k in HP.
His spells both hit on 20 second timers. He alternates them exactly. So you are getting hit with one of his spells every 10 seconds.
Edited, May 5th 2011 10:53am by RandyWoodard