Famicom Mini: Super Mario Bros. 2 Cheats

Each time you beat World 8-4, the game adds a star to the Super Mario Brothers 2 logo on the title screen.
When you have eight stars, go to the title screen and hold A and press START on the controller.

To go to World 9, you must get to World 8-4 without using any warp pipes.
You will only have 1 life when you go to World 9, when you beat 9-4 the game will restart to 9-1 until you lose your life.