Custom Status: Brave or Shy?

That sounds a lot different than I had imagined. Though if it's a debuff, any single target boss vulnerable to it would make Shy even more powerful in that instance than if it were a buff, since applying it to the boss would be equivalent to applying the analogous buff to all four characters in turn. Thus, I suspect any boss that's only one entity would have to be immune to it, and then it would just exist on the heap of various status ailments that aren't worth using in bosses ever because they're all immune to it. Or, if you did make them vulnerable to it, it would be so overpowering that it would be a problem in its own right.

As a debuff, it would probably be better than the analogous buff in randoms, however. Shy as a debuff against the player would also be a decent way to reign in the damage that players do endgame, since a lot of things just generally devolve into "explode the enemy."

Normally, I'd agree that this is pretty OP, but C-Dude's hack philosophy is to make status effects so powerful that they compete with simply dealing damage (despite the fact that "explode the boss" is as viable as it ever was in vanilla).  Almost every boss can be incapacitated or defeated in a single spell cast with the right status effect, and on the buff side you have things like an easily accessible full-party image spell, Runic that lasts forever, and full-party Safe/Shell that are more effective than in vanilla.

Although its effect is certainly powerful, Shy would fit right into ReCast without modification IMO.  For any other hack, I'd hope for it to be implemented more like Octopath (maybe 10% or 20% reduction and it only lasts a couple turns).