Yojimbo?

I don;t remeber what level I was at, but he was hard. I had Rikku as an Alchemist making some mega potions the entire time, Paine as a Dark Night and Yuna as a Dark knight.

Just keep wacking at him until he eats it, make sure Rikku heals you every turn. oh, and a curseproof armor helps a huge amount.