I never was really very good that the Adventure Island games, but I had some tools to help me see some of the later parts of the games anyway.

Like in the third one. I'd go to the title screen

Then press Down, Up, Left, Right, B, A, B, A on Controller 1, which would take me to the Stage Select screen

And, as an added bonus, I'd get some powerups to help.

Which is good, because those later levels are pretty tough.