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Winner's Proof displays exactly thirteen Mushrooms; four in the links and Keychain, two in the handle and the remaining seven on the blade, with one serving as the Keyblade's teeth. The Roman numeral XIII is shown just above the hilt and signifies the thirteen tasks you need to complete to acquire it. The head of the Keyblade forms a heart, bearing resemblance to the Ultima Weapon.
Winner's Proof's name comes from the fact that you have to pass thirteen tests, one for each Mushroom, to acquire it.
Out of all of Sora's Keyblades in Kingdom Hearts II Final Mix, the Winner's Proof has the highest Magic bonus, making it extremely potent when used with a magic-focused form like the Wisdom or Final Forms. When the Keyblade strikes the enemy, the Keyblade produces images of flowers and small stars, some of which include the Mushroom XIII's faces.
 See also