Sonic 2 CD Remix Demo is likely a demonstration or early version of a fan-made game that blends elements of Sonic the Hedgehog 2 and Sonic CD. As a demo, this would be an incomplete version, showcasing only a portion of the total game. It's intended to give players a preview of what the complete remix would offer. This likely incorporates some core mechanics of Sonic 2 and some of the elements, like music or level design, from Sonic CD.  The original games each have their distinct styles, which would be combined in this demo. 

Sonic 2 CD Remix Demo

Sonic 2 CD Remix