Are you talking about the battle where it's versus him and Edea at the end of Disc 2? I think you fight him solo immediately before, and I thought in the second part (with Edea) the idea is he's in a "critical" state the whole time. Then later in the game he's back to snuff so goes back to his normal battle stance.

I might be misremembered some details, haven't played FF8 in a while...