|First Appearance||Super Mario Bros. 2|
|Latest Appearance||Super Mario Evolution|
| Open a keyhole|
Open secret levels
Super Mario Maze
In Super Mario Maze, Keys can be found inside Brick Blocks or behind Thwomps in all levels. They are used to open Keyholes to next levels. When Mario collects a Key, a Key icon appears at the bottom right of the screen.
Super Mario Evolution
In Super Mario Evolution, Keys are found in certain levels. They are placed in Keyholes to unlock secret levels.
New Super Mario World
In New Super Mario World for the Display, keys are used to open locked doors, many of which lead to secret exits. They are also common elements in ghost houses, and may sometimes be required to progress therein. Pressing up in front of a locked door while holding a key will unlock it for the remainder of the time spent in the level.
Keys must be carried, like in Super Mario World, and cannot be taken outside of their respective levels. Carrying one through a Goal Rod will make it disappear and provide a 1UP.