Final Fantasy X Tips

Defeat Seymour Omnis (the last form)
Seymour will have four wheels that have the elements on them. The order it goes in is Red (Fire), Purple (Blizzard), Blue (Water) and Yellow (Lightning). For fire, blizzard and lightning, summon the aeons of that element and only do physical attacks and everytime it's Seymour's turn, he can only do the element that his wheel shows healing the aeon. He'll do dispel some time and then after that, Ultima but this doesn't do much damage. After ultima, he'll change the element. When the wheel turns to blue, have Yuna cast NulTide on the party (in your party could be anyone except for Lulu). Keep doing physical attacks until the next element where you can start the method over again. When I played, Seymour died the second time fire came up and it should for you too.