I personally have beat Ozma, but anyone here want to give other people some tips? I made sure that I got all the friendly animals first and trained to Lv99 with the Yans on Vile Island. Who else has beaten it?

I've beaten it before even though I was cheap with it lol...Just used Zidane, Eiko, Freya, and Quina. All you have to do is used their attacks that do 9999 (Thievery, Frog Drop, and Dragos Crest) and have Eiko throw a Dark Matter. If that doesn't kill it use one more 9999 attack and the bouncy ball will bite the big one...

I got my characters to Lv.99, and before the battle, I made sure eveyrone's Trance gauge was almost full, so one hit would cause a Trance. Plus I equipped Auto-Haste and Auto-Regen. So Ozma used Curse, all 4 of my characters went into Trance (thus curing any status effects and waste time for Regen to fully cure the characters). 4 characters in Trance can bring a world of hurt.