Sonic 1 - Master Edition IV is a fan-made ROM hack of Sonic the Hedgehog for the Sega Genesis, suggesting a significant overhaul of the original game. The "Master Edition" designation implies multiple iterations of the hack, leading to a potentially improved or more polished version.  The gameplay still likely consists of the core elements of the original Sonic game but with changes implemented by the developers.  It is not an official release from Sega.

Sonic 1 - Master Edition IV

Sonic 1 - Fishsticks