trio of 9999 works pretty good, the use lulu's fury overdrive with like fire or the lowest spells and get upp to like 11 or 12 spells which still all do 9999 damage because of the trio. and use all aeons overdrives when he gets too close, use hastega at the first round, then make sure wakka has attack reels and use him with or without the trio. that should work like a charm, if not go train in omega riuns a bit... or monster arena if omega ruins are too hard...