Green Koopa Shells are the shell of green Koopa Troopa that appear in many games of the Mario series and Mario Kart series. Green Koopa Shells remain similar throughout the games but their functions may differ in different games. In the Mario Kart series, Green Koopa Shell serves as a missile and is often called Torpedo Shell, players can launch the shell forward or backward moving the analog stick backward. In Mario Kart 8 developers also made Green Koopa Shells bigger and now they are as big as some of the smaller vehicles. They also changed how Green Shells bounce off the walls making them go more random and harder to predict. A fanart Super Mario progress bar for YouTube with Green Koopa Shell.