Luck, in FFZ, represents your ability to twist fate and the whim of chance to your advantage. There are three main ways to use Luck: Critical Hits, Removing Ailments, and Treasure Rolls.
At the start of any encounter, you have a Luck pool equal to your usual Luck bonus (characters without a Luck bonus do not have a Luck pool). Using Luck for any purpose decreases from the pool, and the Pool is what you use in Luck checks, so any use of this ability decreases from your ability to make a successful Luck check again.
Critical Hits
Luck represents your chance for a critical hit. You can attempt a Critical Hit on any normal basic attack (you cannot attempt a Critical Hit with job abilities). To attempt a critical hit, roll an opposed Luck check (1d20 + Luck vs. the target's roll of the same). If you win, the attack is a critical hit, and you deal double damage. Regardless of the success or failure of this attempt, your Luck pool decreases by 1.
Removing Ailments
Luck allows you to shake off ailments affecting you before their usual duration is up. You can attempt to remove an ailment from yourself as your action on your turn (functioning like the Defend action). Only ailments that end with the combat can be removed with this ability. You attempt to shake off one ailment by rolling an opposed Luck check against the thing that inflicted the ailment (1d20 + Luck vs. the roll of the same). If you win, the ailment is removed. This does not prevent the ailment from being laid on you gain. Regardless of the success or failure of this attempt, your Luck pool decreases by 1.
Treasure Rolls
At the end of an encounter, each character rolls a Luck check (1d20 + Luck) against the DC's of various items of treasure set by the GM. A high roll will net you more gil and better items than you would otherwise get. You may get paltry rewards, or even no reward, if you have used up all your Luck.
