The evolution move-learning simultaneous A+B press glitch, also known as the evolution move-learning script bug, is a glitch in Pokémon Ruby, Sapphire and Pokémon Emerald and Pokémon FireRed and LeafGreen.
If a Pokémon learns a new move just after evolving (for example, Torchic evolves into Combusken at level 16 and tries to learn Double Kick, Mudkip evolves into Marshtomp at level 16 and tries to learn Mud Shot) but it already has four moves, the question "Delete a move to make room for (MOVE)?" will appear.
Then, if A and B are pressed at the same time, the screen will turn black and an invisible "Stop learning (move)?" message will appear.
The player can proceed as if nothing happened, e.g. they can press up and down to move an 'invisible cursor' and cause a sound effect to play, but everything is invisible until A is pressed on the invisible "Stop learning (x)?" message (causing the message to appear visible momentarily) or the invisible "Delete a move to make room for (x)?" message (causes the message to become visible again momentarily and brings up a visible move replacement screen).
If the player backs out from the move replacement screen, the black screen does not occur again (until the glitch is repeated). The player can return to the "Delete a move to make room for (MOVE)?" screen and pull off the glitch again by pressing A and B simultaneously.
The glitch can be done both from within a battle and from outside of battle (possible if a Rare Candy is used). The glitch does not occur if the A and B were pressed at the same time on this box outside of the evolution sequence screen.
In Japanese Ruby, FireRed, Emerald, nothing is visible at all during the black screen. In English Ruby, the red box that surrounds the Yes/No options (this does not appear in the Japanese) is still visible.
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