Co-op has been a staple feature of many Sonic games for decades now. These examples are the best of the bunch.

Sega has filed a trademark for "Sonic Blitz," which some fans believe might be a new game in the Sonic the Hedgehog franchise ...

Sonic 3 set up an explosive sequel with Metal Sonic and Amy Rose – and a new rumor could reveal which game Sonic 4 will adapt.

All players need to do is keep their "Blast Processing" up. Otherwise, the game's visuals degrade way, way down.