Duck Hunt is a classic light gun shooter game for the NES and the game best associated with the NES Zapper. It has three modes: Mode A, Mode B, and Mode C. Modes A and B have you shooting ducks to score points, with A having one duck on the screen and B having two. Mode C has you shooting clay pigeons for points.
For this run, DrD2k9 opts to play Mode A and score the maximum number of points the score counter can display, manipulating the RNG to ensure the desired birds are shot.