A Green Shell is a green-colored Koopa Troopa Shell. They are worn by the most common Koopas and can also be weapons in the Mario Kart Series. When stomping a Green Koopa, it will or hide in its shell or will be kicked out its shell. In both ways, the Green Shell could be used anyway. If it is used in spinoffs or sidescrollers, it always bounces off. This can hurt enemies, but Mario and co. as well.
Mario & Luigi: Sibling Rivalry
In Mario & Luigi: Sibling Rivalry, the Green Shell is a Bros. Item that is used as a weapon against enemies. Two bros. are required to use the item. When the item is chosen, one of the brothers will kick the Shell towards the foe. It will then bounce off the enemy, cause damage, and come to the other player. After each kick, the shell starts moving faster along the ground. The brothers can then repeat this until the player misses a kick, the enemy is defeated, or sixteen successful hits are dealt; in any one of these cases, the Green Shell disappears.
Mario Basketball: Mushroom Tourney
Super Mario Galaxy Odyssey
In Super Mario Galaxy Odyssey, Green Shells once again return, serving the same purpose as they did before. This time, however, they also appear in Item Crystals, and sometimes Koopas will kick their shells down hills or Bullet Bill Blasters will shoot them down hills at Mario.