Mickey Mania: The Timeless Adventures of Mickey Mouse

Level select:
Enter the sound test menu. Set the music option to "Beanstalk1". Set the SFX option to "Extra Try". Highlight the "Exit" option and hold L. A sound will confirm correct code entry. A level selection screen will appear after starting a new game.

Hidden room:
Jump on the cat next to the cabin in level 1. Then, follow the cat down the hole that it jumps into.

Glitch: Double Mickey Mouse:
Go back to the elevator in level 2 and go left instead. You will be in a pitch black room. If you jump enough, you will find some invisible stairs. Jump on these and keep going. Eventually, you will run into another Mickey Mouse. Note: This will freeze the game.