List of Mario vs. Donkey Kong pre-release and unused content
From the Super Mario Wiki
This is a list of pre-release and unused content for the game Mario vs. Donkey Kong.
Hidden e-Reader Levels
Through hacking, the game has 13 e-Reader level entries, 15 in the Japanese version, built-in. The Long Way, One Shot Blue, The Thwamplet, and Danger Flowers seem to be prototypes of The Loooong Journey, Athletic, Thwomp's Fortress, and Dangerous Flower. Laser Panic! doesn't seem to have a prototype level.
Before Mario vs. Donkey Kong 2: March of the Minis, there were plans to have a level editor, but were scrapped. The code remains in the game and can be accessed by cheating. Some elements are broken and saving is not possible.