The immunity bug is a series of bugs in Final Fantasy VI related to status immunity. Immunity is two-way in the game, it keeps the player from applying or taking off a status. Status immunity merely prevents the toggle of a status; the player can't gain the status, but they can't lose it if they already have it either. This is used to make effects from relics and such permanent, except in specific cases where the game won't apply immunity, like Image. However, there are two instances where immunity is ignored. When a character's HP drops below 1/8, they automatically gain Critical status no matter what. If they're immune to the status, they can't get it from Rippler and they can't lose it either, but they can still get it if their HP drops below 1/8.