Sonic for MegaCD is a ROM hack or custom creation possibly based on the Sonic the Hedgehog series for the Sega Mega-CD. While the exact details would require further research, the title suggests a direct adaptation or reimagining of the Sonic franchise for this platform.  Gameplay likely involves the classic Sonic platforming mechanics, high-speed running, and challenges focused on speed and traversal.

Sonic for MegaCD

Sonic CD Warped V1.0.0 (Japan)