Mario Paint is an interactive painting simulator game for the SNES, it comes with a Super NES Mouse peripheral. Within the game the player can do various things, such as paint pictures, make music, or experience the many different surprises the game has to offer.
One of the modes featured is a game called "Gnat Attack", in which the player must use the mouse to swat away gnats, which is what DrD2K9 does here, playing through all 3 levels of Gnat Attack in record time.