? Switch

The '''? Switch, also known as the Mystery Switch, Question Mark Switch , ? Switch Block, or erroneously ? Block''', is a Switch Block that has widely varying effects depending on the context.

Yoshi's Story
In Yoshi's Story, when a Yoshi presses the ? Switch by simply jumping on it, the ? Switch disappears and a part of the level is changed briefly. As the effect expires, the switch's music will speed up. There are panels that also act as a ? Switch and extend the switch's time limit.

Super Mario 64 DS
A ? Switch also appears in Super Mario 64 DS. It appears in the secret level, which is also titled "? Switch" (formerly titled Tower of the Wing Cap). It serves mainly as a one-shot replacement to the original game's three ! Switches. Upon pressing the ? Switch, all ? Blocks in the game will become solid and can be broken open. Whereas the three ! Switches only filled in ! Blocks of their respective color, the ? Switch fill in all ? Blocks, as they are all the same color, red, and the ability that the player will get now depends on the character they are playing as.

New Super Mario Bros.
? Switches later appear in New Super Mario Bros., this time with an orange color. Like the ones in Yoshi's Story, these switches change or add to an area of a level, like adding moving platforms or flipping the entire level upside down. The effects of these switches can be temporary or permanent, varying from switch to switch. One appears in the fight against Mega Goomba, being the only time one is used against a boss.

New Super Mario Bros. Wii
In New Super Mario Bros. Wii, ? Switches reappear with their design from New Super Mario Bros., though they are less common than before. World 6-6 notably features multiple with separate functions.

New Super Mario Bros. 2
In New Super Mario Bros. 2, ? Switches have become more common. Several are used for spawning more coins. They additionally appear in some of the DLC courses.

New Super Mario Bros. U
In New Super Mario Bros. U, ? Switches are again less common. Some act somewhat similar to the giant ! Switch in New Super Mario Bros. Wii by causing red blocks to appear.

New Super Luigi U
In New Super Luigi U, ? Switches are considerably uncommon, only appearing in three stages.

Super Mario Maker
In versions of Super Mario Maker before version 1.30, P Switches in the New Super Mario Bros. U theme have the appearance of ? Switches.

Trivia

 * Although New Super Mario Bros. does have ? Switches in-game, the red ? Switch model from Super Mario 64 DS was left unused in the files of the final version. However, it was used in early prototypes.