Red Key (Paper Mario: The Thousand-Year Door)
From the Super Mario Wiki
The Red Key is an item found in Paper Mario: The Thousand-Year Door. It unlocks the cage the Puni elder was imprisoned in during Lord Crump's invasion of the Great Tree. It is held by an X-Naut in the storage room just west of the prison. After Mario enters the storage room, the X-Naut becomes conscious, mistakes Mario for hitting him, and gets in battle. Defeated, the X-Naut drops this key.
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