So, Metal Sonic 3 & Knuckles (Beta) is one of those weird, half-finished gems from the Sega Genesis era—basically an early version of Sonic 3 & Knuckles, but with Metal Sonic as the playable character instead. You get the same classic zones, but with some janky physics and placeholder sprites that make it feel like you're playing a prototype. The speed’s still there, though, and it’s kinda wild seeing Green Hill Zone with a robotic hedgehog tearing through it.

No idea why this never got a full release, but if you’re into Sonic history or just love digging up obscure beta stuff, it’s a neat little time capsule. Just don’t expect polished gameplay—some of the level transitions straight-up don’t work right.