The early "Sonic the Hedgehog" games on the Sega Genesis had minigame bonus/special stages, such as bouncing around a maze searching for a special gem, or collecting gold rings while running down a tube, and stray from standard gameplay. "Sonic the Hedgehog 3", for example, has a special stage in which Sonic must run around trying to touch all the blue spheres, while avoiding red ones, and interacting with other spheres, who have special properties. This bonus stage actually became its own game. By inserting the original Sonic 1 (or "Sonic Classics 3 in 1") cartridge into the "Sonic and Knuckles" lock-on slot, you can then press A, B, and C, then enter any given password to play the special stage corresponding to that password, which plays exactly like those of "Sonic 3".