Instructions
Cast Hastega with Tidus as the battle starts. This spell will speed up your party, allowing you to get in more attacks in between Seymour Flux's strikes.
Cast Bio on Seymour Flux. This spell will poison him, and he will lose 1,400 hit points (HP) each time it's his turn to attack.
Use Overdrives on this foe to do massive damage. Overdrives are special attacks, and each character in the game can perform at least one particular to them.
Cure your damaged party members with Holy Water or Phoenix Down. Revive fallen characters using the fe spell. If more than one member of your party is KOed, use a Mega Phoenix to revive all of them.
Put Auron on the front line and move other members to the back line if you get a message on the screen that says Seymour Flux is "watching and waiting." He will soon preform a Total Annihilation move, which can easily wipe out most if not all of your team. Cast Protect on Auron to soften the blow. Even if the other party members perish with the attack, Auron can use a Mega Phoenix to revive them.
Attack with Overdrives after Seymour Flux's Total Annihilation attack. He will soon fall.