i beat him with overdrives and just plain old bashing in the head, then i had a power failure before i could save, so i had to do it again.

i casted haste on my party, then poison on seymour, then haste on seymour.

it took HEAPS of damage each time and because of the haste, it damages like 5 times for each turn.

hope that helps if you wanna be cheaty