Winner's Proof

The Winner's Proof (ウイナーズプルーフ) Keyblade is acquired after finding and fulfilling the tasks of the Mushroom XIII, the thirteen Mushroom Heartless scattered around the worlds in Kingdom Hearts II Final Mix. It is granted in the Great Maw in Radiant Garden. This Keyblade, along with Two Become One, is a Kingdom Hearts II Final Mix exclusive.

Design
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.

In Combat
It is the Keyblade with the highest bonus in Magic in Kingdom Hearts II Final Mix, surpassing Fatal Crest from the original Kingdom Hearts II. When striking using the Keyblade, the Keyblade will produce a flower-like effect with a bunch of small stars (some of them have the face of the Mushrooms).

Etymology
Winner's Proof's name comes from the fact that you have to pass thirteen tests, one for each Mushroom, to acquire it.