I just remembered. An absaloutly easy way of beating him is to mix trio of 9999 with rikku and use Slice and Dice. 60,000 health down in one overdrive.

Trio of 9999 ingredients are:

lvl 3 key sphere or level 4 key sphere

mix with:

Wing to discovery, underdogs secret, or a pendulum. i think there is one other im not sure i can remember.

anyway, every hit from then on will do 9999 damage.

I used a wing to discovery as its the easiest to get at that part in the game.