Ok, you got me stumped. I've ran into a few enemies that were able to do this. More specifically, the Tonberry crew in the materia cave. I guess the best way to describe it is zombie status. But as far as I can figure out, there is no way to cure it, or work around it. Great Gospel instantly kills my party, Elixers kill my party, Phoenix Downs kill my party, FullCure kills my party, Remedies miss, Debuff spells miss, and on dead characters, Fullcure misses, Phoenix Downs miss, and Phoenix misses. I've tried to equip Relic Ring, thinking Chef's Curse would reverse it, but I was wrong. I've tried even going opposite, using Kiss of Death and stuff like that of dead members, but to no avail. What's going on? Is it the "you're screwed" status? Is there no way to work around it?