an illustration of a key.

A key appears as an item in Doors to Doom. It is obtained by Mario and Luigi after they find it under a pile of coconuts in the first level of Donkey Kong Jr., Stage One. The key is entirely green, and one side of it is inscribed with "Positively Magic," while the other side is inscribed with "Use once, then discard." Mario drops it in his pocket, and the two continue onward. Later, at the end of Stage Four, they find Bowser in a cage. The padlock is labeled, "Insert green key and turn," and Bowser begs them to let him out. Meanwhile, Dr. Sporis von Fungenstein opens a doorway to peek on them, and Donkey Kong Jr. charges after them. If they do not have the key, Mario and Luigi simply leave through the unlocked doorway. If they have the key, the doorway turns out to be locked and requires the same key as Bowser's padlock. As the key can be used only once, Mario and Luigi then decide where to use their key. If they free Bowser, he promptly says that he intends to leave them behind so that they get attacked by Donkey Kong Jr., but he quickly slips on a banana peel, causing him to crash into Donkey Kong Jr., prompting a fight where the two characters eventually wrestle themselves off the platform. In this case, Luigi removes the key from the padlock and throws the key at the door, but this causes the door to open, revealing a path to Wart's lair. If Mario and Luigi use the key on the doorway, on the other hand, to abandon Bowser, the door ends up leading to the beginning of Subcon instead.