well on the Greater Sphere you probably already know he always counter attacks with Ultima, so just make sure you have youre charaters with high magic defense take the damage if youre planing on taking a hit, and make sure you cast auto life, and just like in every battle start by using hastaga, and if all youre aeons can deal 99,999 then just summon them and attack with them, and dont just rush in with the sister and theire Delta Attack, you can attack them for a couple of turns and still live with all of them and then use Delta Attack, not really sure what else to tell you because, when i fought him my main chracters dealt 99,999 every attack and theire stats were really high
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