Shy Guy

Shy Guys are masked enemies who first appear in Super Mario Bros. 2. They are fairly common throughout the Mario series.

Super Mario Bros. 2
The only Super Mario series appearance of Shy Guys is in Super Mario Bros. 2. Unlike later Mario games, where they work for Bowser, they work for Wart in this game. Shy Guys come in either red or pink (light blue in Super Mario All-Stars and Super Mario Advance) and ride on Autobombs and Ostros.

In its Game Boy Advance version Super Mario Advance, they have a larger sub-species called Giant Shy Guy who also appear in the game.

Super Mario World 2: Yoshi's Island
Shy Guys first chronologically appeared in Super Mario World 2: Yoshi's Island. They can be defeated almost any way.