I’m sure I’m not the only one. The secret was playing the extra hard mode, after that the hardest normal level was a piece of cake.

For those who didn’t know or don’t remember, iirc you held down select while the system and then the game booted up. If you saw a heart somewhere on the screen you were in the secret harder version of the game. I could look it up but I am instead trying to plumb the depths of my memory, it’s been over 3 decades.