From the Super Mario Wiki
The player controls a foil, a type of sword mainly used in fencing. The game takes place in a pitch-black room. The player must cut the gray circles with sufficient force without cutting any of the red ones. Red circles can be avoided by slowly moving the foil past it. If a red circle is cut, the fencer is injured, preventing the player from slicing any remaining circles. In WarioWare Gold, the game takes place in a forest and the player must slice leaves and tomatoes. On difficulty level 3, a bomb will appear.