The debug menu was a feature that was used by the developers to test certain aspects in the game. The developers never removed the debug menu from the game. As a result, hackers were able to access the menu with cheats and codes. The debug menu allows a player to do many different things in the game. The player can gain access to any character, stage, item, and mode in the game. They can also view all the trophies, character endings, and other features. It is highly recommended that it is not used with a memory card plugged in if you have Melee.