Shell Smash (Super Mario 64 DS)
From the Super Mario Wiki
The rules of the game consist of shooting a green Koopa shell against the red ones to gain points. As the shells hit themselves, the user earn points; however, hitting many of them in a row, it is possible to gain more points, even more by knocking two green shells together. The player can shoot up to five green shells to score points. Once the player has no green shells to use, the game ends and the results will be shown. Another similar mini-game involving sliding Koopa shells is Shuffle Shell.
 In-game Instructions
Hit Koopa shells together to score points. Hit many in a row for even more points. Score even higher points by smashing green shells together.