From Bulbapedia, the community-driven Pokémon encyclopedia.
Glitches are anomalies in software programs, including video games. They can cause various problems ranging from the purely graphical to completely wiping entire chunks of saved data.
They are usually caused by problems with a game's code, or from a player doing things the programmers did not anticipate, therefore causing the game to react unexpectedly. Below is a list of glitches in the Pokémon video games.
There are three glitches (the first two are only available in the Red, Blue and Yellow versions; the third one is available in the Gold/Silver and Emerald versions, and the Hall of Fame one is very minor) that do not necessarily always create glitched Pokémon, but are themselves glitches that cause events that would not normally happen in the gameplay.
- Glitch City: A glitch location consisting of mess of random map tiles that changes depending on the location where the player enters Glitch City. 
- Mew glitch: Allowing players to capture any Pokémon (most especially Mew) without modification, and allowing players to catch most of the glitched Pokémon. 
- Pokémon cloning: Variations of the Pokémon cloning trick exist in each Generation of the Pokémon games, each slightly different from one another. The most reliable version is in Generation II. This Pokémon cloning version allows players in the Gold/Silver versions to safely clone Pokémon, assuming they have at least somewhat decent timing.
- Sprite glitch: Glitches that mess up sprites have occurred in all generations (mostly by cheating).
- Surf glitch: allows players to warp to places on the map where Darkrai and Shaymin lie. Note: This only works in some of the first Japanese versions to be released.
- Tweaking: This causes the game to fail to load the map and makes it appear black. Some cases have led the player to places such as Newmoon Island or Flower Paradise if the player goes the right way.
- Rare Candy cheat: An in-game glitch which is the result of encountering a Missingno. or 'M, giving the player over 100 of the player's 6th item (this is also known as the "Old Man Glitch").
- Hall of Fame Glitch: When Missingno. has been seen on the save file, the player's Hall Of Fame is badly corrupted with entirely different Pokémon (players can even see Mew in the Hall Of Fame, whether they've seen Mew or not) and very glitched characters and names.
- Man on roof of Cinnabar Gym: If one does not have the key to the Cinnabar Gym, and surfs on the east coast and returns to land directly infront of the gym, a man will appear on the roof of the gym. A similar effect happens if the player walks into the Vermilion City Gym, walks directly left and then up so that they are facing the bottom-left trash can and press A to inspect it. One of the trainers in the gym will be misplaced and return to his usual spot once the text box disappears.
- Prevented progress: If one evolves their starter Pokémon before they obtain their Pokédex from Prof. Oak, the game will assume that, since they have 2 Pokémon registered as caught, that they already have a Pokédex, and will not allow them to proceed.
- Invisible PC: There is a hotel in Celadon City that resembles a Pokémon Center on the inside. In the top-right space of the area that the player can walk on, there is an invisible, usable PC.
- S.S. Anne Truck: If a player gets a Pokémon which knows cut (HM01) through a trade before actually obtaining HM01 during gameplay, the player will be able to skip the S.S. Anne. Later on, after obtaining HM03 (surf) and teaching it to a Pokémon, the player will be able to surf around the vicinity of the S.S. Anne. On one piece of land, there will be a truck which has no apparent purpose.
- Q Glitch: A glitch enabled by the Pokémon Q (and Charizard 'M) which allows Pokémon stored in the PC to swap moves and stats.
- ZZAZZ glitch: A bizarre side effect of the Mew glitch using a Pokémon with a special stat of 251, 252, 254 or 255. When this is done, a Glitch trainer will appear. In the Red and Blue versions, after battling the Glitch trainer, numerous abnormalities will occur, including the player's name being turned into "ZZAZZ" and 3 of the player's Pokémon being turned into Bulbasaurs. It has been known to erase a player's saved game. The abnormalities which occur in the Red/Blue version are not the same as those which occur in the Yellow version.
- Glitch dimension: Turns everything into strange, random colors and slows the ability to see the party screen and changes the "Poké" in PokéGear to random symbols. It is usually activated by first using the Coin Case and then speaking to the Machop at Vermilion City.
- Dratini glitch: After the player speaks to the Dratini in Blackthorn City and uses the Coin Case, the Coin Case's display will change what the coin case says from "Coins: ..." to "Which move?he pp of" permanently unless the game is turned off.
- "Reset the clock" glitch (Gold/Silver only): A glitch that allows players to manually reset the games' clock by entering a password unique to the player's ID and the amount of currently owned money. It was fixed in Crystal.
- Celebi Egg Trick: Allows players to capture Celebi using a number of steps.
- Hill glitch: East of Mauville City there is an Aroma Lady that will battle the player. If the player stands right behind the hill in her line of sight, she will see the player and walk onto the hill and stay there until the player leaves the area. This does not happen in Emerald due to her being a part of a double battle in the same area.
- Berry glitch: Freezes the growth of any berries which have been planted but not harvested, often occurs after the game has been owned for a year or played for over 100 hours, though not always.
- Pomeg glitch (Emerald Version only): A glitch involves negative HP.
- Colosseum Master Ball glitch: Also known as the Infinite Ball Glitch; it is a glitch which involves battling different Pokémon in order to keep the number of balls in the bag from going down.
- Acid Rain: Rain falls on the battlefield when a Pokémon is knocked out with Pursuit during Hail or Sandstorm.
- Main article: Glitch Pokémon
A glitch Pokémon is a Pokémon that exists in a game due to a programming or level design oversight or for beta testing, and as it was not intentionally placed inside the game by Nintendo or Game Freak, it might be hazardous to saved data. They were originally supposed to be place-holders for unused Hex-addresses in the game. Glitch Pokémon are to be avoided due to the risks they may pose to a player's save file.
This is a chart of all 24 known glitch Pokémon that can be found in the wild in the Red, Blue and Yellow versions without using a cheating device:
Non-obtainable glitch Pokémon
The following Glitch Pokémon can only be found by using a cheating device such as GameShark and cannot be caught using the Mew glitch or any other known in-game trick.
The following glitched Pokémon can be found in the Gold/Silver versions, but require GameShark to complete them. (Note: after capturing these Pokémon, the game's graphics have been known to falter, and the player will find themselves in a Glitch City-like area.)
Glitch Pokémon gallery
In this screenshot, a Ditto transformed into the player's Q, and then the player sent out a Spearow
H POKé, a difficult-to-catch glitch Pokémon
"Five question marks", a glitch Pokémon which accounts for the hexadecimal slots 000, 252, 254 and 255 in the Gold/Silver versions
Glitch egg, which accounts for the hexadecimal slot 253 in the Gold/Silver versions
7g being encountered in the Yellow version
A glitch attack, or glitch move, is much like a regular attack except the results are often undesirable. Like with glitch Pokémon, glitch attacks were not programmed into the game on purpose and many have been proven to cause damage to game cartridges. The only widely known ones are those for Pokémon Red, Blue and Yellow. Glitch attacks are sometimes displayed as TM attacks (TM01-TM55 and HM01 to HM05), but some have no name or a glitched, unreadable name. Some attacks are of known glitch types (see list below), but most have either no type or an unknown type, and are often referred to as "Super Glitches" (see List of glitch moves).
There are ways to teach glitch attacks to certain Pokémon without usage of a cheat-code device such as GameShark, however, most of the time only glitch Pokémon will learn glitch attacks.
One way of teaching a Pokémon in Generation I a glitch move is trading to a Generation II game a Pokémon that will evolve by trading at a level when it will learn an attack in the next generation game, and then trading it back to the Generation I game. For example, trading a level 50 Haunter from Pokémon Red to Pokémon Gold will make the Haunter evolve into Gengar. Since it is level 50, it will learn Destiny Bond. If you trade it back to Pokémon Red, it will still have the move, but the game won't recognize it since it is a Generation II move.
Also, the move Thunderbolt, when used in some Ruby and Sapphire cartridges, may cause the game to freeze.
There are many different glitch types that are found to be the types of several glitched Pokémon. The most well known are:
Aside from Glitch City in Generation I, there are several other areas which can only be reached by way of a glitch in the games. Examples of this are areas in the Sevii Islands that are retrievable via their index number pointer, however, do not have any other data. Sevii Isle 8 and Sevii Isle 9 are the only index number areas which have actual map data.
In the Generation II games, it is possible to get an item called the Teru-sama, the only description of which is a lone question mark. Generation III likewise has a mystery item. Both of these seem to have been placeholders just in case more slots for items were ever needed, something that came true with the Clear Bell in Crystal and the various newer items introduced just in FireRed and LeafGreen and Emerald, which register as the Teru-sama and mystery item if they are somehow moved into Gold and Silver or Ruby and Sapphire. There is also the Seal Bag, a glitch item obtained from the Generation IV GTS glitch.
The Teru-sama is a glitch item, but can be transformed into the GS Ball if it is given to Kurt in Azalea Town to capture Celebi in Ilex Forest. This works in the Japanese, English and European versions of Pokémon Crystal Version.
Glitch trainers have been known to occur in the Red/Blue/Yellow versions. They are usually found if the player's name contains mostly special characters. There are also several special stat numbers used in the Mew glitch which cause glitch trainers to appear. Glitch trainers frequently use Glitch Pokémon in battle.
- Missingno.'s special stats for the Mew trick vary (see ).
- The Yellow version Missingno. is different from the Red/Blue Missingno., but both share the same name. For the Yellow version Missingno., using a Pokémon in Method #3 of the Mew glitch with a special stat of 31, 32, 61, 62 , 63, 67, 68, or 69 would make it appear(). Missingno will revert to level 0 if leveled up to over level 255 with Rare Candies or to level 100 if it fights in battle and wins.
- The Pokémon 'M, 3TrainerPoké, Charizard 'M and Q are the only known catchable glitch Pokémon that cannot be directly caught using the Mew glitch. Other glitches can be obtained by messing with the game link cable during a trade. 'M and 3TrainerPoké cannot be caught using the Mew glitch because the special stat required for method #3 of the Mew glitch is 0, a number which no Pokémon has. Charizard 'M and Q cannot because Q can only be found by evolving a 44Hy, and Charizard 'M can only be found by trading a Q. The special stat numbers which would cause Charizard 'M or Q to appear in a Mew glitch-type battle freeze the game.
- The glitch known as ".4" can freeze or crash the game if it uses a certain glitch move. If the game is saved while this move is in .4's moveset, the data may be corrupted, making it impossible to continue and forcing the player to start a new game.
- The 24 catchable glitch Pokémon, plus the original 151 Pokémon, brings the total number of catchable Pokémon in the Red/Blue/Yellow versions to 175.
- The characteristics of one Glitch Pokémon usually do not apply to its Red/Blue or Yellow equivalent. For example, LM4 will evolve into Clefairy and then immediately into Nidoking, whereas its Yellow version equivalent, 7g, has no evolutions.