A green Koopa Troopa from Super Mario Bros. 3 in Super Mario All Stars (SNES)
Mario Bros. (Arcade/NES/GBA)Edit
The original "Shellcrawler" appearance from the Mario Bros. game. They were replaced by Spinies in the GBA version.
Super Mario Bros. (NES/SNES)Edit
Koopas are turtles that can be stomped on but it retreats in it's shell instead of disappearing. Green Koopa Troopas walk off of blocks, but red Koopa Troopas turn instead.
Super Mario Bros. 3 (NES/SNES)Edit
They reappear here with similar behaviour to Super Mario Bros. for NES.