Automatically uses Potion when damaged.
Description
Auto-Potion is a support ability in Final Fantasy IX that every permanent party member can learn. The user consumes a Potion or a Hi-Potion (if there are no Potions in the inventory) each time damage is taken from an enemy for the cost of 3 Magic Stones.
Obtained[]
Auto-Potion is learned from numerous equipment pieces for variable amounts of AP; Vivi learns it the fastest at 10 AP, while Zidane, Freya, Eiko, and Amarant learn it the slowest at 30 AP.
Auto-Potion is learned from numerous equipment pieces, but one early and easy source is from the Mythril Vest for everyone but Steiner and Freya, found in Cleyra's Trunk 
and stolen from the Antlion boss in Cleyra. Gold Choker teaches Auto-Potion to everyone, first synthesized in Treno. Running Shoes also teaches Auto-Potion to everyone, obtained for defeating Tantarian and found in the grandfather clock in Quan's Dwelling after bringing both Quina and Vivi there after the party has the Blue Narciss.
Mechanics[]
The user consumes a Potion or Hi-Potion each time damage is taken from an enemy. Auto-Potion does not use up a turn. If the party has no Potions in the inventory, they will use a Hi-Potion instead. If the player has neither in inventory, nothing happens. If the character has Chemist, the Potion or Hi-Potion heals for double its normal power, but this is bugged in the PC and Xbox version (see Chemist article for details).
If the character is afflicted with Zombie, they will damage themselves with the Potion they use. If the character is afflicted by a status ailment that prevents them from acting, Auto-Potion will not trigger. If more than one party member has Auto-Potion, and the party is hit by a party-wide attack, the users will take turns using Potions onto themselves one by one. Auto-Potion only activates when taking damage from an enemy; it does not react to losing health from Poison or being hit by an ally.
Use[]
Auto-Potion helps keep the party's health topped up, but depletes the party's healing item stock. Healing items are fairly cheap and plentiful as item drops and steals. As all other action is halted when Auto-Potion triggers, it can get annoying when the battle is constantly being interrupted; this pause can also work for the player's favor if coupled with Auto-Regen, which keeps ticking during animations, meaning whenever damaged, the party both regains HP from Auto-Potion as well as from the pause when Regen was allowed to tick for "extra" while the rest of the action was halted.
Auto-Regen is the superior passive healing method, healing for more and not interrupting the flow of battle, however, Auto-Potion is available earlier. The player could use it until they get Auto-Regen, especially in portions of the game where white mages are not available, like Alexandria Castle when rescuing Garnet, Oeilvert, or Mount Gulug where Dagger's abilities are still hampered and Eiko is not in the party.