The player has to kill 128 Tiny Marios in this event. Each of the Marios are tiny, which can make them difficult to hit, but almost any attack will kill them in one hit. Marios will start coming down five at a time. This event is tedious, so items like the Warp Star and wide-attacking Pokémon are helpful since they can KO multiple Marios at a time.
The name of this event match is a reference to the series of experiments to test technology that was eventually used in later games from Nintendo, as well as a sequel to Super Mario 64 that was never released.