Which bug fixes do you consider indispensable?

I think the critical bugs are the Sketch glitch, Evade bug, and Cherub Down killing Interceptor. Anything else is minor or something you'll have to deliberately exploit. That said, important balance bugfixes are Genji Glove damage, Vanish/Doom, permamorph, Muddle/Smoke bomb, and stacking immunities.

Then there are the severe but very unlikely bugs like Jump softlocking the game in certain conditions, or the Kutan glitch, airship glitch, 52 game overs glitch, tent glitch, cid timer glitch, etc, that you'll never see unless you go out of your way to break the game.

There's also a whole bunch of minor bugfixes that I'd rather have than not have, but essential? Nah.

Finally there's a whole bunch of balance fixes that aren't technically bugs, just bad design. But I won't get into those or QoL stuff even though I think they're more essential than most bugfixes.

EDIT: I knew I'd forget some stuff. The Enemy AI FC command bugfixes, Suplex damage, pincer/back randomosity, status timers, are all pretty important bugs because they affect normal (not intentionally breaking or exploiting) gameplay.