Shellcreeper

Shellcreepers, also known as Turtles or Shell Creepers, are low-slung, green-shelled turtles that roam the sewers of the Mushroom World. They first appeared in Mario Bros.

Mario Bros.
The Shellcreeper is the first enemy to appear in the game. They come out of the pipes (like most other enemies).They also resemble Koopa Troopas. Hit it from below to flip it over and then run into it to defeat it. If Mario or Luigi fail to run into it, the Shellcreeper jumps out of its shell (and reveals that it wears shorts), flips its shell over and then continues moving, this time faster than before. Jumping on these enemies will result in losing a life.

In the remakes of Mario Bros., Spinies replaced Shellcreepers, so new players would not jump on the Shellcreepers, mistaking them for Koopa Troopas.

Mario Power Tennis
Shellcreepers, as with the other Mario Bros. enemies, appear in the background of the stage Mario Classic Court.

Super Smash Bros. Brawl
Shellcreepers, as well as Sidesteppers, appear on the stage Mario Bros., a stage based on the classic arcade game. They comes out from the upper pipes and is dangerous to touch when they are walking and may sometimes come out of the shell if they are jumped from underneath, as in the arcade game. A new feature is that characters can pick them up and throw them at others, sending them to fly directly sideways. This becomes very useful, as the low ceilings stops the characters from being KO'd normally. Oddly enough, the Shellcreepers are powerful enough to KO opponents at low damage percentages, and the shells appear to be unblockable by shields.