Um
I beat him like this
Dark KNight x2
Alchemist
Stock up on Potions and Hi-Potions and be sure that your Alchemist knows Mix and Dark KNights know Darkness, and have thier health really high *not sure whether you NEED to but it'll help you stay alive*
Have you Alchemist and Dark Knights if possible have something that'll hasten them and have Ribbons on them or something to protect against status ailments
When the battle starts, you should maybe use something to lessen the magic and physical attacks *there's an item lunar curtain or something*
Have your Dark Knights use Darkness and Alchemist mis the high potions and potions to make mega potions
Depending on how much damage it takes away, the battle will go faster
*you'll find this combo works for a lot of fights*