What you do is get six Pokemon that know Metronome and fight six Pokemon that know Metronome. Metronome is the only attack allowed to be used. If a Pokemon runs out of Metronome PP before fainting then switch to another Pokemon. If neither team faints completely then the winner is whichever team received the least amount of damage.
Has anyone ever had a Metronome battle? I used to do it all the time on Pokemon Stadium. The randomness of it was awesome.