Protect against Status Ailments and you'll be good.

I had Steiner, Zidane, Vivi, and Garnet yesterday to beat him, Steiner died pretty quick, but I just had vivi casting a focused flare (didn't have doomsday), Garnet summoning Bahamut (she tranced and for some reason summoned him twice a turn or somethin like that) and had Zidane attack, eventually he went down, 1st try, alot easier than I thought.

Good luck.