House Key (Super Paper Mario)
From the Super Mario Wiki
The House Key is an item appearing in Super Paper Mario. It is an Important Thing found in Merlee's Mansion. It is inside the far right room on the second floor. It is used to open a door on the first floor and at the same time, free Gnaw.
When Mario enters the room, nothing happens. If the player keeps going to the right, they can eventually find a button that will trigger the windows closing and a spiked ceiling descend when pressed. Mario must flip to 3D to avoid getting crushed by the ceiling and hop on it, using it as an elevator to get to some platform above. Navigating them, with the help of Boomer, the player will eventually reach a treasure chest, which contains the house key.
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