You don't even get any rings…
YOU DON'T EVEN GET ANY RINGS!!!

It's the boss of the Underground Zone, the first Zone in Sonic 2 for Game Gear. You can't damage him yourself, you have to let those ball bearings hit him. Each one bounces at a different height and speed and comes right on the heels of the last one, and they are actually somewhat hard to avoid (especially when you're a kid) because jumping on tilted ground launches you in the direction of the tilt. Topping it all off, boss Acts in the game have no rings whatsoever, so one hit and you're dead. It was a perfect storm of frustration.