Final Fantasy Wiki
FFXII_-_Glitch_with_potion_and_Phoenix_Down
The glitch in action

The Phoenix Down glitch in Final Fantasy XII involves using a healing item (such as Potion, Ether, Handkerchief) on a party member who is KO'd before the item can be used, and is immediately revived with a Phoenix Down.

To trigger the glitch, the player must give a healing item to an ally who dies at the same moment, while another ally has a gambit to use a Phoenix Down on a KO'd ally; because item use has no Charge Time the Phoenix Down is used immediately, and the two allies will end up using an item on the reviving ally simultaneously. For an unknown reason, the healing item will heal the target multiple times when used simultaneously with a Phoenix Down.