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The Wario Key is an item in the game Super Mario 64 DS. The Wario Key was created by Bowser, who gives it to Chief Chilly and his gang after they capture Wario. After Luigi was rescued by Mario, Luigi headed to the third floor of the Princess Peach's Castle. Upon entering the room with the giant mirror, Luigi can grab a Power Flower, granting him the "vanish" ability. The intangible Luigi was able to then pass through the mirror and jump into the painting of Wario. In the painting world, Luigi confronted and defeated Chief Chilly, claiming the Wario Key in the process.
The Wario Key is a gold key about Luigi's size. It has a giant "W" in the center with a Wario's Cap on top. After Luigi unlocked the door that Wario was locked behind, Wario became a playable character and Wario's Caps became available in courses.