Tiny is a status ailment in the Paper Mario series.
Paper Mario
Certain enemies such as the Hammer Bros. have the ability to shrink Mario. When Tiny, his attack power drops by three. It is indicated by a pink, white, and green circle above Mario.
Paper Mario: The Thousand-Year Door
The effect returns in this game, but this time around, it only docks Mario two attack points, lessening the severeness. It is indicated by a very small face.
New Super Mario Bros.
In this game Mario and Luigi can turn Tiny by using a Mini Mushroom. This ability helps them, go through small passages they normally can't. Like going in Mini Warp Pipes.