Sonic 2 on the Genesis codes work on this version too. On the Sega Genesis there are codes that unlock a level select, debug mode, and one that gives you all 7 chaos emeralds from the start.
SEGA has announced Sonic X Shadow Generations downloadable content “Sonic the Hedgehog 3 Movie Pack,” which will be included in the game’s Digital Deluxe edition. It will launch on December 12.