P-Switches (originally known as Switch Blocks, alternatively written P Switch) are objects found in several Super Mario games. In the New Super Mario Bros. series, they are usually found inside Brick Blocks or Question Blocks. They temporarily turn empty Brick Blocks into coins and vice versa. In some cases, they also make Blue Coins appear (also temporarily). If the player collects all the blue coins before they disappear, a clapping sound is heard.
P-Switches first appear in Super Mario Bros. 3. They invert blocks to coins and coins to blocks, but they have a limited time.
In the Super Smash Flash series
The P-Switch appears in Super Smash Flash 2 on the stage Mushroom Kingdom III as a stage hazard. It will occasionally appear at one of the edges of the stage, and if the player attacks or steps on it, it will destroy all the brick blocks on the stage.