From: pjbasis | #164
I read something that almost convinced me Yu Yevon is worthy of final boss status.
Basically the idea is it was supposed to be a "puzzle" battle, because essentially he heals himself for more damage then you're capable of doing.
As you don't have Aeons at this point, and most games likely won't have any Break Damage abilities, 9999 damage is about as much as you're capable of, and he auto heals for 9999.
Obviously it's very easy to circumvent this with any move that deals more than one hit, mainly overdrives, Reflect and Zombie status.
Or standing around for a while because he can't kill you
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Mistake you're making - overlooking the fact that we might not want to be saved.