My mistake - it's the Synthesis battle.
They share data, so it's harder
Not quite. The Jenova AI sets some globalVars that Sephiroth's preBattle AI then reads from. But it's not like data is preserved from one battle instance to another, and you can remove the references to these globalVars without any issues.
Anyway, the question for Thao is:
- do you want to stop Sephy getting more HP when Jenova has been hit by KOTR?
- do you want to change how Sephiroth gets a HP boost for each Lv99 party member?
- do you want to stop Sephiroth losing HP for each time Bizarro's head was killed?
If you want to stop all of these behaviours, and have Sephiroth's HP set by the stats that Hojo (and now Proud Clod) manipulates, then delete lines 0 to 0x14A in Safer's preBattle AI script, using Proud Clod.