Sidestepper

The Sidestepper is a type of enemy in the Mario series of games. Sidesteppers are crabs. They first appered in Mario Bros., an arcade game.

Mario Bros.
The first level they appear in is 2-1, making them one of the earliest enemies Mario ever fought. Mario can defeat a Sidestepper by jumoing underneath them, causing the platform they are on to damage them. Two hits are required to defeat one. After one hit their face changes to a made one. Later in the game a blue variety appears.

Mario Clash
Sidesteppers later appeared in Mario Clash. Two shell hits were required to defeat one.

Mario Advance: Super Mario Bros. 2
In the Game Boy Advance remake of Super Mario Bros. 2, crabs resembling Sidesteppers appear before Clawgrip is fought. A bubble resembling the kind Wart uses transforms them into Clawgrip.