EarthBound/Battle Debug Menu

The in-game and boot-up debug menus have been common knowledge for quite a while, but the third debug menu managed to stay hidden for 15 years until December 2010 when it was found by two different people within days of each other! This debug menu is the same as the glitchy one accessed by the "Show Battle" option on the boot-up debug menu, but it's fully functional.

Penguin from Starmen.net created a patch to access the battle debug menu. The patch can be downloaded below. The archive contains patches for both headered and unheadered versions of the EarthBound ROM.

General controls
With the patched ROM, simply press the Y button on the overworld to access the battle debug menu. The battle debug menu will start in party adjustment mode.
 * Press the Start button to enter the battle mode.
 * Press the Select button to go into enemy adjustment mode.

Party Adjustment/Effect Viewer Mode

 * Left and Right will change the configuration of your party.
 * Up and Down will increase or decrease the levels of all party members by one.
 * The X button will change the levels of all party members to match the enemy/enemies' levels. It's unknown how the game exactly calculates the levels when there are multiple enemies present.
 * The B button will display different fade-in and fade-out effects, e.g. the battle swirls.
 * The A button will display battle effects, i.e. animations for PSI attacks and Jeff's battle items.

Battle Mode
Battle mode starts the fight with the enemy. You can press Select to go into item giving mode. The controls for item giving mode are as follows:
 * Press Up and Down to increase or decrease the item number by 1.
 * Press Left and Right to increase or decrease the item number by 10.
 * Press B to cancel.
 * Press L or A to confirm and then choose which party member you want to give the item to.

Enemy Adjustment Mode
In enemy adjustment mode, a textbox will show the number of the current enemy group.
 * Press Left and Right to choose which digit of the enemy group number to change.
 * Press Up and Down to change the digit.
 * Press L or A to confirm the enemy group selection.
 * Press B or Select to confirm the enemy group selection without reloading the enemy graphics/background. This will most likely result in glitchy graphics.

There's no known way to exit the battle debug menu. Even winning or losing in battle mode will just bring you back to the party adjustment menu.