We're going really retro with this article's SAGE 2020 spotlight, it's time to look at Sonic 2.5! This fan game is very simple. As the creator, Slow the Snail, puts it, it's "a fan game that aims to mix elements of my favorite Classic Sonic games, Sonic 2 and Sonic 3". Sonic 2 gets the "music, levels, and nostalgia", combined with Sonic 3's "characters, power-ups, transformations, cutscenes, level transitions", and more.
Currently, the demo is just a small level, although a bigger level is coming soon. Still, if you want to download and play it for yourself, go here.