Official FF6: Beyond Chaos thread (randomizer)

Although the Zombie specials are also easier to prevent, since they check for immunity. Zombied characters can also tank things, so the effect is diminished if the special attack is used again (it might just hit the same character). Personally I'd consider the instant death special to be more annoying than the Zombie one because of that. Muddle could also be a candidate, as a Muddled character can wipe your party if they are powerful and using something like Ultima or Meteor. But again, it's easier to prevent. Stop is unpreventable, and more difficult to remove, but doesn't require healing afterwards, and it can wear off without intervention eventually.

Personally I still consider death to be the most dangerous of the "normal" effects (i.e., nothing wacky like Dance).