The Game Genie was a device created by Codemasters that attached to the bottom of NES games. The device would bring users to a screen before starting the game which allowed them to input codes that would modify the game by starting them at different levels, giving them powerups or just completely changing the game itself. Some users of the Game Genie went as far as to create new games out of old ones. Super Mario Bros 3 was used with the Game Genie to create a ROM hack. The Game Genie is a powerful device and this ROM emulates the code screen.