I won't be satisfied now without a Lin, Su and Toph scene. ;A;
I found Seymour rather easy tbh. I just max out the overdrive of all of Yuna's summons and hit him with one after another. He banishes them on his next turn but if they're overdrives are maxed you can use a summon before he does so. >=D
2nd Chance, once more, and leaf bracer. Of course abilities that recharge your mp from damage and such also help but aren't exactly needed. Those first main three always ensure you have one hp and can heal.
"Those swampbenders can't take a punch" x'D Old Toph is picking on the swamp people too.