Mario Clash is a Virtual Boy game produced by Nintendo in 1995. It is heavily based on the original Mario Bros. The objective of the game is to knock all the enemies in a particular level off ledges. This is accomplished by hitting them using Koopa shells, of which there are always two Koopas -- if one shell is knocked into a pit, another appears to take its place. The majority of Mario's enemies need to be hit on the side (i.e. with a shell thrown from the background while the enemies are in the foreground or vice versa). Despite being heavily promoted by Nintendo, the game failed to live up to expectations, in part due to the lack of a feature to save your progress in the game between sessions. However, you can select whatever stage you want to begin play in before the game starts. Mario Clash is notable for being the only Virtual Boy game to date that was made into a microgame in the Wario Ware series.