EXP bonus abilities

Level Up (レベルアップ, Reberu Appu), also known by various other names, is a support ability, mostly found on pieces of equipment, namely accessories, that usually doubles the amount of Experience Points a character earns from battles. It is an ability usually acquired around midway to late in the game.

Final Fantasy IV
Level Lust is an ability gained from an augment found in the Hummingway Home in the game's Nintendo DS version. It is a support ability that increases the amount of EXP gained from battles by 50%. It can be obtained multiple times via the New Game Plus feature.

Final Fantasy V
EXP Up is a Level 2 ability found only in the Advance version, and is part of the Cannoneer job class. The ability allows characters to gain 1.5x more EXP after battles, and requires 150 ABP to master.

Final Fantasy VI
Level Up is an ability found in EXP. Egg, which can be equipped by everyone. It is found in Darill's Tomb, in a hidden room after completing a puzzle. It can also be obtained from the Coliseum by betting a Tintinnabulum, or morphed from Vasegiatta, Marchosias, and Galypdes. It doubles the amount of experience gained from battle.

Final Fantasy VII
Level Up is an ability found on the EXP Plus Materia. At Level 1, it increases EXP earned by x1.5, and at Level 2, by double. The EXP Plus Materia can only be obtained after Meteor is summoned at the Gold Saucer's Wonder Square, for 2000 GP. The effect doesn't stack.

Final Fantasy IX
Level Up is an ability that can be learned by everyone. It is learned through Iron Helm, Egoist's Armlet, Extension, Fairy Earrings, Pearl Rouge, and Rosetta Ring. It increases the experience earned by 1.5. Mastering this ability requires 75 AP for Zidane, 30 AP for Vivi and Dagger, 50 AP for Steiner and Amarant, 40 AP for Freya, 60 AP for Quina, and 65 for Eiko. 7 Magic Stones are needed to equip.

Final Fantasy X-2
Double EXP is an ability found on the Lady Luck Dressphere mastered for 80 AP, and Covenant of Growth Garment Grid by passing through the yellow gate.

Final Fantasy XII
The party can double their EXP intake by equipping the Embroidered Tippet accessory. It can be stolen from the Coeurls on Tchita Uplands, or bought from Old Archades for 5,000 gil.

Final Fantasy XII: Revenant Wings
Knowledge to Power is an ability learned by Ashe that increases the amount of EXP gained for the whole party, and is learned from the Embroidered Tippet accessory. How much the accessory increases EXP intake appears to depend on the battlefield.

Final Fantasy Tactics
Accrue EXP is an ability that allows a character to gain EXP as they move. It is learned from the Arithmetician class for 400 JP. EXP Boost, also known as Gained EXP UP is a Support ability in Final Fantasy Tactics. It is learned from the Arithmetician job for 350 JP. A unit with this ability will receive one and a half times the experience from every action they perform.

Dissidia Final Fantasy
Several pieces of equipment offer EXP +% bonuses, though are more commonly found on the chocobo accessories, namely Chocobo Down (EXP +20%), Chocobo Wing (EXP +50%), and Chocobo Feather (EXP +100%), all with a 30% chance of breaking after battle. The weapon Excalibur II also offers EXP +100%, but considering that the player does not get this weapon, nor can use it, until a character reaches Level 99, it is mainly pointless except for increasing the effect of EXP to HP/Bravery/EX Force.