Gil bonus abilities

Gillionaire, also known as Millionaire, Gil Farmer, Gil Plus, Gilfinder, and Smart Riches, is a recurring ability in the series that lets the player earn more gil from battles.

Final Fantasy IV
Gil Farmer is an augment in the DS version that can only be obtained in Troia, in the dressing room of the Members Only area.

Final Fantasy IV: The After Years
The Gil Band is an accessory that multiplies the amount of money the party earns by 1.5. It is found equipped on Edward Chris von Muir in Edward's Tale. In the Crystals, a Gold Tail can be traded for a Gil Bandv2, which doubles the amount of money earned.

Final Fantasy VI
Although it is never mentioned in-game, the Cat-Ear Hood headgear provides the Gillionaire ability which doubles the amount of gil the party earns from enemies. It can be obtained by betting an Impartisan in the Dragon's Neck Coliseum and can only be equipped by Relm.

Final Fantasy VII
The ability can be found on the Gil Plus Independent Materia. Due to a bug in the game, Level 1 will never produce the 1.5x amount that it is supposed to, and will always double the amount of gil earned from battles as though it were mastered. The ability is not stackable. Gil Plus can be purchased in Gold Saucer's Wonder Square for 1,000 GP.

Final Fantasy IX
Millionaire is an ability exclusive to Quina that increases the amount of gil the party earns from battle by 50%. It can only be learned from Yellow Scarf for 100 AP.

Final Fantasy X
Gillionaire is an ability that can be found in, or customized onto, a weapon. It requires using 30 Designer Wallet items to customize. Rikku's Celestial Weapon, Godhand, has this ability when fully-powered.

Final Fantasy X-2
Gillionaire is an ability found on the Lady Luck dressphere. It takes 100 AP to learn, and it can only be learned after mastering Double EXP. It can also be accessed via the Horn of Plenty Garment Grid by passing through the red gate on the grid. The ability is stackable.

Final Fantasy XI
Gilfinder is a Thief job trait that increases the amount of gil enemies drop, usually by 150%. The ability is learned at level 5, and is enhanced by Assassin's Culotte, Palmer's Bangles and Andvaranauts.

Final Fantasy XIII-2
The Gilfinder, Gilfinder II and Gilfinder MAX passive abilities can be found on various accessories and recruitable monsters, the most prevalent of which being the Durable Collector's Catalog, being bought post-story from Chocolina using a regular Collector's Catalog (which can be won from Serendipity chocobo racing) among other ingredients. Gilfinder II is most easily found in the Chunerpeton enemy as it is present from level 1.

Final Fantasy Crystal Chronicles: Echoes of Time
Smart Riches slightly increases the amount of Gil picked up by players, and can be customized onto pieces of equipment through using the Gil Mania jewel.

Dissidia Final Fantasy / Dissidia 012 Final Fantasy
The Beckoning Cat accessory increases the gil earned from battle by 20%. When three pieces of Gold Equipment are worn, they activate the Glorious Gold combination, raising the gil earned in battle by 50%. Certain Calendar Bonuses increase the gil won, from 10% up to 100% depending on the level of the bonus. In Dissidia 012 only, the Qu'bia Tail accessory found only in the Labyrinth increases gil earned by 100%.

Bravely Default
More Money is the specialty support ability of Merchants. It lets the characters earn 1.5 times more money than normal.

Trivia

 * 10% Gillionaire is the name of an Achievement in the Windows Phone version of Final Fantasy, obtained by collecting 100,000 gil.