You would think something like that would be easy to find out. From what should have been a quick search I found 926 - 1005. How it picks I do not know.

Knowing that, Demi and Drain Life will do ~250 damage and Lich and Demi2 will do ~500 damage. Apparently he is also vulnerable to Silence, if that helps at all.

You're not going to like this, but there is another battle immediately after this one in which ninjas help a lot (Though not necessary)