|'''This article is a summary page for different variations of a glitches, etc. when talked about as a whole.|
It is caused by the game's inability to detect the system as GBC compatible, due to this detection relying on the now broken assumption that the console's bootrom (the piece of software responsible for, among other functions, displaying the Game Boy logo) had just finished running.
It is so named due to being one of the earliest discovered applications of the Coin Case glitch and hence a Generation II parallel to Generation I's Glitch City, despite the fact it does not place the player within in a glitchy collection of tiles in the way that Glitch City does, nor do they share any technical details.
Despite the name's origin this effect is not unique to the Pokémon games, but can potentially happen in any GBC game; in fact, the term has seen moderate acceptance outside the Pokémon glitch community. Conversely, it is not an issue on Nintendo DSi software due to a completely different implementation.
ExplanationWhen the game is run on a Game Boy Color or Game Boy Advance/SP, the console's bootrom passes control to the cartridge with register 'a' initialized as 0x11, and this value causes the game to use Game Boy Color mode. Other consoles' bootroms initialize the register 'a' differently: The original Game Boy and Super Game Boy initialize it to 0x01, and the Game Boy Pocket and Super Game Boy 2 initialize it to 0xFF.
GBC games would usually check for this value at the very beginning of game startup, near the entry point. For example, Pokémon Gold sets memory address $FFE8 to 0x01 if the game is run on the Game Boy Color or Game Boy Advance/SP, or to 0x00 if the game is run on another system. (A soft reset will skip this initialization.)
Glitch Dimensions occur because after the unexpected reset the register 'a' is no longer 0x11, and this causes the game to think that the system used is not a Game Boy Color or Game Boy Advance/SP.
As a result, the game will no longer update any color palettes for the background map or for sprites. Those color palettes will be carried over from the moment before the unexpected reset. For example, if triggered with the Coin Case glitch, the previous screen will be the item pack UI, which is covered mostly with a blue palette, but also has some regions with green, red, and pink palettes in order to display those colors. After the glitch is triggered, the game would be "stuck" in a blue palette, and those colored regions can be seen on various screens.
More information can be found here.
The game's display will be colored in a glitchy way, usually with "glitched color blocks". The Ho-Oh on the title screen of Pokémon Gold will "show its true colors". (Interestingly, this does not apply to Pokémon Silver.) This is caused by the game displaying the title screen legendaries with the player sprite's palette. Normally both legendaries are displayed with a white-and-brown palette so that only their silhouettes can be seen, but Ho-Oh's sprite actually have enough details that will become visible when the same brown colors in the palette are replaced by different colors in the player palette, and Lugia's sprite only uses one of the white colors and one of the brown colors anyway. The fact that the player's orange-and-red palette closely resembles Ho-Oh's "true colors" is merely a coincidence.Three unexplained side effects of Pokemon glitches by Crystal_ On Pokémon Crystal, the "This Game Pak is designed only for use on the Game Boy Color." screen will appear. The girl in the Goldenrod Department Store who enables Mystery Gift will tell the player that Mystery Gift requires a Game Boy Color. The Mystery Gift option will not appear on the Continue/New Game/Option screen.
Examples (in Pokémon Gold/Silver)
Coin Case methodMain article: Coin Case glitch
Using the Coin Case glitch (basically having the player listen to a Pokémon cry and then use the Coin Case), certain Pokémon cries will cause glitch dimensions when the Coin Case is used (when not following the arbitrary code execution steps for Machop, Bellsprout, and other Pokémon). Some may require having not switched item pockets after listening to the cry, or having switched item pockets.
Machop was the most known example that causes a glitch dimension, but other Pokémon like Omanyte and Horsea can do it.
Move 00 methodA glitch dimension can be caused when accessing the fight menu with a move 00 in the first position, but this is luck based; the game may also freeze.
Trade a Ditto with the Cooltrainer move to Pokémon Gold/Silver. Access the fight screen.
The game may reset in different colors than if a Coin Case Glitch Dimension was used.
Walk through walls methodUsing a walk through walls code, the player can cause a Glitch Dimension by out of bounds of the first floor of their house. Walking out of bounds can cause very variable effects depending on (at least) the tile you stepped into, meaning a Glitch Dimension may not happen through this method.
Example (in Pokémon Crystal)Using the Pokémon Crystal glitch moves hex:FC (TM52 in Generation I) and hex:FE (TM54 in Generation I) may cause a Glitch Dimension to happen.
In Pokémon YellowIn Pokémon Yellow, a Glitch Dimension has happened before when trying to encounter Yellow regular Missingno. on the opponent's side.
A Glitch Dimension can be guaranteed on Pokémon Yellow with the code 0178DFDF. The player must press A in the opening at a time such as when a black silhouette of Pikachu can be seen 'running forward'.
Another Glitch Dimension possible with arbitrary code execution is brown and is nicknamed "Pokémon Brown Mode".
Other types of unexpected resets
Normal resets: The game resets with seemingly no known side effects.
Altered gameplay: The game resets, but with side effects not previously mentioned. These tend to happen less commonly. Example: Pokémon Crystal's type 0xFF mail.
This Game Pak is designed only for use on the Game Boy Color.