Instructions
Equip your party with an ability that make enemies drop rare items more frequently, such as Lucky Lucky. You receive a higher chance of finding rare items when two or more party members equip a special ability.
Equip your party with weapons and accessories that also increase the chances of an enemy dropping a rare item. Equip Sora with the Sweet Memories Keyblade from the Hundred Acre Wood, Donald with the Meteor Staff from Port Royal and Goofy with the Genji Shield won in the Titan Cup at Olympus Colosseum. Give a member of your party the Lucky Ring accessory, which is won in the Pain and Panic Cup at Olympus Colosseum.
Seek out and destroy the enemies that drop Serenity Crystals. Only the Samurai, Assassin, Berserker and Sorcerer Nobodies drop Serenity Crystals. The Berserker and Samurai Nobodies are found in Twilight Town while all four Nobodies are found in The World That Never Was. Without any bonuses from abilities, weapons or accessories, there is only a 4% chance that these enemies will drop a Serenity Crystal so you will have to fight several enemies to obtain one.
Collect 500 synthesis materials to receive a free Serenity Crystal. This bonus is not dependent on what type of materials are collected, just that 500 in total are collected over the course of the game. The tally is cumulative, so synthesis materials you use to create weapons and items will still count towards the total.
Collect at least one of each type of Twilight Material to receive another bonus Serenity Crystal. The Twilight Materials include Twilight Shards, Twilight Stones, Twilight Gem and Twilight Crystal. Find Twilight Shards from Gambler and Dusk Nobodies, Twilight Stones from Dancer Nobodies, Twilight Gems from Assassin Nobodies and Twilight Crystals from Sorcerer Nobodies.