Super Mario Bros. and Duckhunt were actually seperate games when the NES was first released. The NES originally was packaged with two controllers, Duckhunt and the zapper gun, and a game called Gyromite which used the R.O.B robot (which was also packaged in). Nintendo made the robot so they could market the NES as a "toy" and not a "video game" system. They were afraid that people would be scared off if they thought of the NES as a mere gaming system, due to the Video Game Crash. After the NES became a success though, Nintendo no longer had any use for the robot, so they stopped packaging it and Gyromite with NES systems and started packaging the Super Mario Bros/Duckhunt combo games instead.