It is required to access certain areas in X-Naut Fortress in Paper Mario: The Thousand-Year Door. There are three different colors of Card Keys in this game.In Super Paper Mario, a single Card Key can be found in Floro Caverns. It can be used in order to access the processing room eventually leading into an encounter with Dimentio and O'Chunks. Dottie can shrink the party to go through the tiny hole that leads the Card Key.
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