Using Poltergeist's Essence (Null Elec, Null Panic)
Hamaon
Agilao
Restore
Resist Ice
Resist Dark
Diarama
Long, somewhat annoying fight, but quite manageable with the right skills. Probably could've been done at a lower level but would've required good luck to not get booty blasted by mud in the first phase.
He does Babylon's Curse every 4-5 turns, so you have to do enough damage to kill a tentacle in that time, which often means you have to not get sticky with mud. Guarding on Babylon Curse turns help tremendously avoiding the ailment. Doing this at level 41 gave me enough buffer turns to consistently kill tentacles even if I get muddied or have to heal. Make sure to top off everything once the tentacles are down.
Phase 2 was pretty easy; although he no longer randomly casts Zionga, the guaranteed magatsuhi turns being Mazionga means I always have two turns to refill mana, which is more than enough with Restore and gem usage to not have to worry about mp.