Sidestepper

A Sidestepper (also known as a Crab) is a red crustacean that scuttles sideways. They are one of the first enemies the Mario brothers ever encountered. If made angry, a Sidestepper will bare its teeth and begin to move much faster than normal.

Mario Bros. (Arcade 1983)
In the Mario Bros. arcade game, the Sidestepper is the second enemy that the Mario encounters (the first being the Shellcreeper). They are first seen on Stage Four. Like other enemies, Sidesteppers emerge from pipes and walk on the stageâ€™s platforms. They move the same speed as a normal Shellcreeper. When hit from below, a Sidestepper will become angry and speed up. Hit the Sidestepper again from below to flip the enemy over, then run into the crustacean to defeat it. If Mario or Luigi fail to run into a Sidestepper, it will flip itself back over and move even faster than before.

Sidesteppers also appear in all remakes of Mario Bros.

Mario Clash (Virtual Boy 1995)
In this game, Sidesteppers come out of pipes and scuttles sideways (just like before). Hit it in the front or back with a Shell to turn it sideways, then hit it in the side with another Shell to defeat it.

Mario Power Tennis (Nintendo GameCube 2004)
Sidesteppers return in Mario Power Tennis. On the Mario Bros. Classic court, the original enemy sprites are used instead of modern sprites. During a Gimmick game, a Sidestepper might walk across the court and trip a character.

Mario Kart DS (Nintendo DS 2005)
After years of using generic crab obstacles in other Mario Kart games, the crabs on the Beach stages in this game are angry Sidesteppers.

Other Names
In the Japanese version of Mario Bros., the Sidestepper is known as the Kani-San.