Blue switch (Super Mario Galaxy)

A Time Switch is an item that appears in Super Mario Galaxy 2, usually during levels with unusually fast-moving obstacles. During gameplay, Mario or Luigi must Ground Pound them. Once Ground Pounded, the entire screen will turn black and white, and the music will sound very slow and distorted, as if it were coming out of a radio. The main effect of hitting the switch, however, is that it will slow down all the obstacles around Mario or Luigi. They can allow them to pass under a Thwomp or jump on a fast-moving platform with ease. The switches only last for a few seconds though, so the player must move quickly to make it through the level in time. Time Switches appear in only three galaxies: the Space Storm Galaxy, the Clockwork Ruins Galaxy, and the Stone Cyclone Galaxy.

Trivia

 * Note that in the Beta version of Super Mario Galaxy 2, an earlier version of a Time Switch was shown as a sort of "side-flipping" switch, as opposed to looking more like a ! Switch, as it does now.
 * Sentry Beams' lasers, Amps' electricity, Electric Fences, Water Shooters' bubbles and Coins don't turn black and white when a Time Switch is pressed.