For GameShark codes used to access the Debug Menu, see here.
The debug menus are elements of development that were accidentally left in Super Smash Bros. There are four menus: System debug, Battle debug, Falls debug, and Unknown debug. Within these menus, the player has control over various aspects of the game, including unplayable characters, unplayable and single player stages, and more. In order to get to the debug menus, a GameShark device must be used.
This menu contains various out of battle functions. Within it, one can play every sound and piece of music in the game and view every transition. Sadly, these two options appear to be the only ones that still function correctly. The others appear to do nothing.
Menu item
Description
Values
Continue
Makes the menu disappear. It reappears if "start" is pressed.
—
rumble
Has no function in the final release, but was presumably for testing rumble intensities.
Min=0; Max=10; Increment=1
frame
Has no known function.
Min=0; Max=8000; Increment=1
STOP RUMBLE
Has no function in the final release, but was presumably for stopping rumbling caused by the "rumble" option.
This menu contains options for starting 1P Game and Versus Mode matches. Characters such as Master Hand and Metal Mario can be selected here, and they can play on each stage in the game, including Meta Crystal and Battlefield. Pressing start begins the match.
The stages used for the "Board the Platforms" bonus game. There is one for each character. The game crashes if these stages are called through the debug menu.
"S" Stages
This option is only active if the mode is set to "1P Game". It sets which event to place player 1 in. This includes 1P Game stages and challenger approaching events.
A very unstable menu, the Falls debug menu was most likely used to test the results screen, although it does nothing now. The game may randomly crash upon loading this menu for no known reason. There are 12 options in the menu, 3 for each character. Finish is repeated twice per character. The top one will crash the game if scrolled past 4. The bottom one can go out to 65536. Dead also ranges from 0 to 65536. If "A" is pressed, the battle debug menu is loaded, although changes made to the Falls debug menu appear not to affect the match or results screen in any way.
Unknown debug menu
This mysterious menu appears to have no function whatsoever. It lacks the interface found in the other 3 menus and appears to respond randomly to any button presses, throwing overlapping UI elements on the screen. This menu differs considerably from version to version.
The unknown debug menu in Super Smash Bros.
The unknown debug menu in Super Smash Bros.
Trivia
Super Smash Bros.'s debug menu contains two voice clips of Ness, one saying "PK" and another saying "Starstorm", as well as another clip of Captain Falcon saying "Come on!" (similarly to the start of his Blue Falcon move), suggesting that Final Smashes were originally intended to appear in the game. Masahiro Sakurai later confirmed in an interview that he did intend to implement Final Smashes in Super Smash Bros., and that the voice clips were intended for that purpose.