Luck is a Special ability found on Rikku's section of the Sphere Grid. It costs no MP to use. Although it claims to increase the party's Luck stat, it does not give the full effect of higher Luck. Each use of Luck adds 1% to accuracy and 1% to the chance of landing a critical hit; unlike a genuine Luck stat increase it has no impact on evasion or on the chance of receiving a critical hit. This can be stacked up to five times.
The ability returns in Final Fantasy X-2 for the Lady Luck dressphere. It costs 30 AP to learn, and 8 MP to cast. It increases the Luck stat of a single target by 10 points. Upon learning it, a group-cast version of the ability, named Felicity, is unlocked, costing 40 AP to learn and 8 MP to cast. It increases the Luck stat of the entire party by 3 points.