Shellcreeper
Shellcreepers, also known as Turtles or Shell Creepers and known as Kame-Sans (or Mr. Turtles) in Japan), is a low-slung, green-shelled turtle that roams the sewers.
Mario Bros.
The Shellcreeper is the first enemy to appear in the game. They come out of the pipes (like most other enemies). 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.
In the remakes of Mario Bros., Spinies replaced Shellcreepers, so new players would not jump on the Shellcreepers, mistaking them for Koopa Troopa's.
Mario Power Tennis
Shellcreppers, as with the other Mario Bros. enemies, appear in the background of the stage Mario Classic Court.
Super Smash Bros. Brawl
Shellcreppers, 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 is 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 tham at others, sending them to fly directly sideway. This becomes very useful, as the low ceilings stops the characters from being KO'd normally.
Trophy Information from Super Smash Bros. Brawl
Shelled enemies Mario and Luigi faced back when they were plumbers. They had to be bumped from below to flip them over and then kicked off the stage. The last one on a stage turned from green to red and raced really fast. If one got flipped but not sent off, it would eventually right itself and move at high speeds. They were simply called "turtles" in Japan.
Notes
The Shellcreeper is clearly a conceptual ancestor of the Koopa Troopa. Aside from both being turtles, Shellcreepers also wear shorts when outside of their shells - something the Koopa Troopas started doing in Super Mario World 2: Yoshi's Island (in Super Mario World, Koopa Troopas wore undershirts and shorts).
