Sonic 2 Return of Shadow (First Public Release) is a ROM hack of Sonic the Hedgehog 2 for the Sega Genesis. Information on the creators is usually found within the ROM's description or through fan communities where it's shared. This hack most likely centers around Shadow, a character introduced in later Sonic games, giving him a prominent role within the Sonic 2 engine.  This usually means altered level designs, potentially new playable characters, and altered gameplay to fit the Shadow character theme.  Its distribution method would be through fan-made ROM websites and gaming forums. The base game, Sonic the Hedgehog 2, was developed by Sonic Team and published by Sega in 1992.

Sonic 2 Return of Shadow (First Public Release)

Sonic 2 Recreation Part One