Make sure you understand the title of this glitch - don't try this out if you want to beat the game with everything. Because you'll fail. Now, play as Peach and get an item or badge while playing as her. Don't put the it in the magic box. After the last time you get to play as Peach, you will not be able to recieve the thing that she was carrying. Voila. It's as simple as that... but it really does not sound fun.
Submitted by: Maestro