The Mystery Gear, along with the Casual Gear, access the Joke Weapons of the characters. However, the weapons created by this gear reflect the true personality of the character, so some of them are of a more serious nature than the weapons created by the Casual Gear.
Weapons
III. Xaldin: Wyvern (Lance)
VI. Zexion: Dear Diary
VIII. Axel: Conformers
IX. Demyx: After School
X. Luxord: High Roller's Secret