I can't really say Ozma is challenging...This isn't really a hard battle comparing to other FF series like Endless Twilight said; however, some luck WILL be needed...who knows...he attacks fast sometimes...grrrrr

My party was Zidane/Garnet/Freya/Amarant
and only Zidane and Garnet surpassed 70s, while the other is around 50-60s. I didn't really bother with Auto-Life or Auto-Potion, instead, I had Auto-Regen with shadow absorbing armors or 100% against shadow attacks. My Amarant and Garnet were the support characters in the battle, I leave most damage to Freya and Zidane(after Zidean stole everything of course), my Thievery was around 9000+ damage. I use Amarant to give Auto-Life, and his Curse is useful. You can use Curse on Ozma until he is afraid of shadow attack, and I even equip Amarant with Return Magic; therefore, whenever Ozma used Doomsday, I can absorb shadow attack, while he hits himself with shadow attack, which can do around 9999.