Sorry if I haven't got the level names correct, I don't think I can remember them exactly. But the two that gave me the most trouble are Rolling Gizmo Galaxy (one of the green star galaxies) and the rock boss when orbited by the Daredevil comet.
Finally did the Rolling Gizmo Galaxy, after losing dozens of lives falling off through my own stupid fault (just didn't have the patience to be careful!), but still haven't done that boss. It's mega hard, but I know I can do it. I just do something stupid each time, like run into a boulder instead of away from it. Grrrrr.
You know a game is great though when tough levels don't put you off, and you still appreciate and respect the levels and the game.