From Bulbapedia, the community-driven Pokémon encyclopedia.
The glitch dimension (as it is often referred to by fans) is a glitch in Gold and Silver Versions. Unlike some other glitches, this glitch is merely for altering the visuals of the game, and will not negatively effect or delete the saved file once it is executed.
Several different things can happen upon activating this glitch, one being that the game freezes upon activating it. The other is that the screen turns white with a small purple rectangle in the top right-hand corner and the game restarts with different colors. When activated, it alters the colors of everything from the area the player walks around in to the wild and Trainer battles. Also, it slows the processing speed when trying to view the player's party Pokémon when not in battle. Pitch black places like Dark Cave will be illuminated without the use of the move Flash. The Poké in Pokégear changes to ど◀ when the player enters their Pokémon selection.
Interestingly, the Ho-Oh on the title screen of Gold Version changes from a silhouette to a fully colored Pokémon.
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Performing the glitch
Coin Case method
- Main article: Coin Case glitches
Either talking to the Machop in Vermilion City, the Machoke in the Goldenrod Department Store or viewing the Pokédex entry of Machop, Machoke or Machamp then use the Coin Case will cause the game to enter the glitch dimension.
Trading a Pokémon with the glitch move -- onto a Gold, Silver or Crystal, then using -- in battle will cause the game to enter the glitch dimension.
The glitch causes the game to reset unexpectedly. When this happens it repeats the process used at startup to determine what type of Game Boy it is running on. This process relies on the fact that different models leave different information in memory at startup. Since the game was already running, that information is no longer present, so the process fails and believes it is running on a classic Game Boy.
This can be confirmed by talking to the girl in the Goldenrod Department Store who enables Mystery Gift, who will explain that it requires a Game Boy Color, and from the error message displayed after performing the glitch in Crystal.