If you take it too lightly and just jump away for the easy and fast multiple hits, you can easily find yourself forced to fall into oblivion.
As far as hard while rushing, Chemical Plant, I think, deserves an honorable mention. Definitely the hardest to master, and I've never quite been able to do so. Sonic 2 - I'll put in a vote here for the boss after Wing Fortress Zone. I think it's similar to Spring Yard in how it can go smoothly, but feel this one is more consistently annoying on subsequent playthroughs. But the last few times I played it went pretty smoothly, so I'm going to have to go with LABYRINTH ZONE here. It seemed like if you didn't make it through perfectly and hit him enough times when he landed, you'd be sure to lose. Sonic 1 - I want to agree with you on Spring Yard Zone's boss, as I used to get stuck on it.
