Select sound test. Set the music to beanstalk 1, FX to extra try. Go to the exit option and hold L for seven seconds. You will hear a noise. Go back to the main game screen.
At the first level, jump on the cat that's next to the cabin. The floor boards will give way and the cat will fall through. Walk on the spot where the cat fell and you will fall through too. There's a secret room with marbles you can collect. To get out, push aside the boxes.
Before the end of the second stage, you can take a short detour and meet another Mickey. At the top of the elevator shaft, you normally follow the path to the right to get to The Mad Doctor's Lab. If you get back on the elevator, it will take you on a different path. Once you meet your twin, the screen will fade, and you'll appear outside the lab.