Along with the main game, the disc for Sonic Generations on Xbox 360 and PlayStation 3 will also contain a port of the original Sonic the Hedgehog, Sega have announced.
You’ll need to unlock the port before you can play it, though. Completing each Generations stage will earn you points. Once you have enough points, you can go to the in-game Skill Shop and purchase the “Sega Genesis Controller,” which unlocks the game.
Additionally, points can also be spent on infinite continues for Sonic the Hedgehog, once you’ve unlocked the game.