ReCast FF3: War of the Magitek

I didn't even try Suplex or Slash against bosses since I assumed they wouldn't work, but IMO they are problems as well.

It doesn't matter if Garnet and Pearl have different effects if nobody ever uses them because Onyx is far and away the better option 90% of the time, and the only time it isn't is when you can kill the boss by punching it (again, excluding bosses that null poison). It's a very similar problem to vanilla's Ultima, though with different caveats.

I feel like the best case scenario (if you're willing to consider ASM work for this) would be for bosses to have a flag that causes all of these attacks to only deal 10% (maybe 15%) of their current HP. That way these attacks are still usually the most powerful option at the beginning of the fight compared to the numbers I've been able to achieve with other means, but good damage output is otherwise still useful. Even then, Tetra-Slash would be broken; IMO that should be something completely different.

My thoughts about an ASM free solution: if Terra, Celes, and Relm were the only people who could learn it, then the spell balance is less broken, but the character balance is more broken. The only way that I can see this working without any other changes is if Onyx is learned at level 70+ for all three of them. TBH, if somebody's that overleveled then the game balance doesn't really matter all that much. I could see it being okay if Suplex/Slash do 2/16 against everything; this would make them useless in randoms, but that's probably not a big deal because they still have a solid and common use case in boss fights. Again in this scenario, I think Tetra-Slash wants to be something completely different.