Stock up on Antidotes, Softs, and Al-Bhed Potions from Rin. Customize Poison Ward and Stone Ward onto your armors. If one of your characters get stoned, just use an Al Bhed potion. Besides healing 1,000 HP, they'll also cure poison and petrification. IIRC, deal damage up close until he inhales. Than have Cid pull back, and start dealing damage with your distance people. Of course, Haste will help you wonders. When he gets down to 16,000 HP, he'll cast Haste on himself and you'll never be able to slow him down. Just try to avoid his Breath attack at all costs. Oh, and make sure you have some extra Al Bhed potions after the fight, seeing as how you'll have to fight your way through a horde of enemies without the ability to save in between.