P Switch

P-Switches (also known as P-Switch Blocks in Super Mario World, New Super Mario Bros. and New Super Mario Bros. Wii) are items found in Super Mario Bros. 3, Super Mario World, New Super Mario Bros. and New Super Mario Bros. Wii. When pressed, a P-Switch changes something in the stage for a limited amount of time. This includes:

One rather confusing thing is that a brick block with an item inside it will look like a coin but act like a block. This confusion was removed in the Game Boy Advance remake of Super Mario Bros. 3. In Super Mario World, the gray version of the P-Switch makes most enemies turn into Silver Coins. Collecting eight of these coins awards Mario a 1-Up. Collect one more for a 2-Up. After nine coins, Mario will earn 3-Ups for each additional coin. In New Super Mario Bros. Wii they're sky blue
 * Turning Brick Blocks into coins.
 * Turning coins into brick blocks.
 * Changes enemies and Munchers into Silver Coins. (Super Mario World gray switches only)
 * Allowing Mario to access a silver Door.