Koopa Shell

When you jump on a koopa once, the hide in their shell of fall out of there shell. Now you can use the koopa shell.

New Super Mario Bros
In this game, there are green shells, red shells, and blue shells. Green and red shells are used as projectiles. Blue shells allow you to be shell Mario.

Mario Kart
In this game, there are also red, green, and blue shells. The green shells shoot strait forward and bounce right of walls. Red shells are homing. Blue shells fly up to the person in first place and hits them. When a blue shell hits first place, it gets hit by the power of a bob-omb.

Super Mario World
In this, if you throw/kick the shells, it's just a normal shell. But when Yoshi puts one in his mouth, he gets special abilities. Green Shell-just a projectile for Yoshi Red Shell-when Yoshi spits a red shell out, he breathes fire. Blue Shell-It give Yoshi little wings to fly with. Rainbow Shell-When Yoshi jumps and lands with one of these shell in his mouth, it makes the ground quake.