Keys are items that appear in the Mario series, and usually are used to unlock doors and gates. They have appeared in many of the platform and RPG games in the series.
Super Mario Bros. 2
Keys first appeared in Super Mario Bros. 2. Mario used them to unlock various locked doors. They can be picked up and must be carried to the door they unlock. They can be thrown at enemies to defeat them. If Mario picks up a key, a Phanto will appear and try to attack him. Throwing the key or using the key on a locked door makes the Phanto disappear.
Super Mario World
Keys are sometimes found in Super Mario World. They are hidden in often hard to reach locations, out of the way from the usual path that Mario has to take. If Mario is able to a find a key, he can bring it to its corresponding keyhole, and exit the level early and find an alternate route on the map. The key can also be kicked at enemies. Mario can carry the key, or have Yoshi hold it in his mouth.
Super Mario World 2: Yoshi's Island/Yoshi's Island DS
Keys are used in Super Mario World 2: Yoshi's Island and Yoshi's Island DS to unlock various doors. Yoshi can only carry five eggs while holding a key. They are often found in crates, held by balloons, and hidden in potted plants. They are required to unlock minigame doors.
In Luigi's Mansion, keys are used to unlock the various doors of the mansion. Usually, they are found in treasure chests after clearing the room of ghosts, but that is not always the case. For example, the first key obtained in the Wardrobe Room is found on top of a clothes rack. After beating boss ghosts and Vincent Van Gore, Luigi gets special keys that allow him to access the next area in the mansion.
Super Mario Galaxy/Super Mario Galaxy 2
In the Paper Mario series and other RPGs
Keys are also used in the Mario series RPGs as items that can be used to open doors and sometimes chests throughout the games. They keys themselves are often found in chests or are obtained through other people. While most chests don't require keys to open, some doors in dungeons may be locked, typically those leading to special rooms or boss battles.
- The Key found in Pikmin 2 has the design of the key in Super Mario World.