Sonic 3: Robotnik's Washing Machine

The main danger is the fact that you're stuck under water. You'll only die to that boss once, I would say. It's called Dr. Robotnik's Waddlepool Machine in Sonic the Comic. If you are just about to drown, wait till the music cuts out and then exit the water,. if you then spin that out, it will start playing the Sonic and Knuckles music. On just the Sonic 3 cartridge it does that. Because you don't hear that music on the Sonic 3 and Knuckles combined.