I used zidane freya and quina to defeat ozma.
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Quina had some kind of strange spell that could cure that attack with status effects i think,

angel snack - it uses a remedy on each character but be careful you need to have enough in your inventory or it wont use any

quina is also good for a few other skills such as mighty gaurd and frog drop (provided you caught atleast 100 frogs) ,

one extra little note .. if you cause any prebuffs on such as protect or shell ... you can trick the game into making it last longer ... just have one character sit on their menu screen (go into items or something) when you or ozma is doing an attack that has a long animation ... the animation will continue but the counter for the buffs wont count down .. also works with doom and gradual petrify .. only thing is you have to have the game on wait not active .. and when you are in the menu your atb bars wont be filling up so as soon as the attacks are done get out of the menu so you can fill up for your next attack

i use my steiner to solo him :S he nearly had earned all abilities and ofcoures max lvl i cant remember much more

I used Pumice and shadow armor so his doomday heal me (that my basic strategy so i dont get a weight with a whm around i use vivi doomday to heal me )and other part is steiner freya and luck