Custom Status: Brave or Shy?

I think you misunderstood "Shy". It's a debuff, it would reduce the target's damage output by 1/2. While that is somewhat similar to Shell/Safe, it is target-oriented rather than self-oriented. It would also probably be a single-target spell.

I did come up with a way to make monsters block the status, though. I can use the Suplex special effect and the "Block Suplex" flag, since I removed that restriction from the actual Suplex and it is otherwise unused. There's no way to protect the players from it, but at least some bosses would be able to resist the spell.

I'm leaning towards Shy, mainly because the red palette makes the character look like they're blushing (Celes even uses it on that first scene on the Blackjack).