Sonic Multi is a mysterious title with limited information available. Without further details, it's difficult to determine if it's a completed fan-made game, a ROM hack of an existing Sonic game, or perhaps a prototype.  Further research into online ROM hacking communities and databases would be necessary to understand its origin, gameplay style, and overall development status.  This title highlights the vast and sometimes cryptic nature of fan-made Sega Genesis games. 

Sonic Multi

Sonic Megamix 2.0 