Ideally 3x BRDs rotated in until you all have 2x Mad/Min/March, all eat attack food, all use DD 2hrs, either inside WHMs to cure or fast outside ones, but healers are important.
BLMs also do decent damage, but not on the level of melees.
MNK > WAR > RNG/SAM > DRK/DRG > THF/NIN/BLU/BLM
Treat it like a Kirin burn, but with 1-2 CS Stuns, shouldn't last the first CS, but it might, so have a second take over before the first is done to compensate.
I read his regen may be weaker in the day, but I'm not sure about this one.
Keeping people alive is as important as doing "leet damage", as given time and a small army of healers, an ally could probably just melee it to death anyway.
Don't forget you can wait as long as possible grav kiting for people, he doesn't build resist to gravity (or very slowly due to being earth based).