My advice would be that if you're having trouble on that boss, go into the airship, and look for co-ordinates X 69~75 Y 33~38. This should take you to a place called Omega Ruins.
In this place, you shoud get roughly, or at least, 1 sphere grid point per battle. If your character has double AP, you can get up to 4 grid moves. In this way you can level up like crazy, and after a few hours, can deal at least 9999 damage with each of your starting or favourite characters.

I also just let the background music in that battle get to me and I went mental in the battle and slaughtered him lol.

well this is very tricky for me 2 but i became lucky. have all aeons and people with overdrives use the magie sisters overdrive kills the first 1 easy then pay all of your money to yojimbo (or just about, u dont get 2 buy anything once he is deafeated) and really hope that u use his killer move (my name) after you kill him yuyevon is easy u always have auto life on every1 and can never die