In order to end this battle victoriously, one will undoubtedly have to be familiar with Ozma's AI.
To begin with, Ozma chooses its actions depending on whether its turn count is an odd or an even number. In the former case, it will use either Flare Star, Meteor, Doomsday, Flare, Holy, Death or Absorb MP. If its turn count is an even number on the other hand, it will employ either Curse, Mini, Level 4 Holy, Level 5 Death, Curaga or Esuna. Additionally, most of these attacks are used only if certain conditions are met. For instance, Ozma will cast Holy only if at least a single character does not absorb the Holy element and is not affected by the Reflect status.
Apart from its main attack script, Ozma is one of the few enemies in FF IX to be provided with counter attacks. Not only may Ozma utilize the Berserk spell twice during the course of the battle, namely when its HP is reduced to a value less than 40,000 / less than 30,000, but also, much more frustratingly, may Ozma counter any(!) action executed by characters with its highly potent Curaga. Still, the probability with which Ozma will actually counter with Curaga is inversely related to its HP and ranges from approximately 13% to a staggering peak of 50%.
As a consequence of Ozma's disposition to employ Cuarag as a generic counter attack, one should better be lucky not to have to witness too many / any of Ozma's Curaga counter attacks. Since there is moreover no means to guard oneself against the Berserk status, one will have to resort to the Auto-Reflect ability to definitely prevent that status ailment.
Even though Ozma's attack pattern is notorious for its unpredictability, it is indeed possible to manipulate it quite immensely thanks to Freya.
Interestingly, while none of one's characters are on the field, which is the case when Freya is the only non-KOed party member and during her Jump animation, Ozma will use exclusively either Doomsday or Curaga (I have not found out what happens if Ozma's MP are used up since both attacks cost MP (Someone would like to investigate this?)).
If Ozma's HP are not lower than 27,767, it will use only Doomsday, otherwise it will use only Curaga.
Being in possession of these pieces of information, it should not be too complicated anymore to devise a suitable strategy to single-handedly break everyone's favorite long-expired, breathtakingly ugly, nuclear-waste-repository-flavored bubblegum ball...
Finally, would someone like to comment on how I named my characters?
1) Stolen Materia Remix (FF VII OST)
2) The Battle for Everyone's Souls Remix (Persona 3 OST) http://www.mediafire.com/?fvbj61j3m9t7o2s
3) Last Labyrinth Remix (FF BC OST)
4) Eternal Harvest (FF IX OST)