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A wild Mew being found using the Mew glitch
The Mew glitch (also known as Trainer-Fly glitch) is a famous glitch found in all of the Generation I Pokémon Game Boy games. It was first reported in 2003, but was used previously by many who knew it. This glitch famously allows players to easily catch any Pokémon in the game, most notably Mew (hence its common name). In addition, it is the easiest way to catch many unique glitch Pokémon.
The first documented and most commonly known method to perform the Mew glitch involves the Gambler on Route 8, who is facing north towards the Underground Path entrance, and the Youngster on Route 25 who is facing north and has a Slowpoke on his team. The player must have defeated neither Trainer before, and must also have a Pokémon who can use Fly on their team.
The player must stand directly beneath the Underground Path entrance door, at which point the aforementioned Gambler will be exactly one tile offscreen. It is recommended that the player save the game at this point in case a mistake occurs in a future step. The player then can begin the glitch by taking one step down, and pressing and holding the Start button while the step is occurring. The Gambler will be scrolled onto the screen during this process and the player will enter his line of sight, but the start menu should appear before the Gambler "sees" the player.
From the start menu, the player must Fly away (with the most convenient location being Cerulean City). If the previous steps have been performed correctly, the Gambler will have the indicative exclamation mark appear above his head, but then the Fly animation will begin before he can walk up and challenge the player.
After landing in Cerulean City, the Start, A, and B buttons will not function properly, as the game believes that the player is currently in a battle. From here, the player should walk to Route 25 and battle the aforementioned Youngster. Importantly, the Youngster must walk up to the player to initiate the battle, or else the game will freeze.
After battling the Youngster, the previously disabled buttons will now work again. The player must now return to Route 8 (with the most convenient method being Flying to Lavender Town and heading west). Upon entering the Route, the start menu will appear by itself; closing the start menu will immediately begin a battle with a wild Level 7 Mew.
If the game is saved and reset during the glitch, or the player returns to Route 8 after Flying but before battling, or if any battle occurs or any NPC is interacted with between the time of the Youngster battle and the Mew encounter, then the glitch will not work and the game must be reset to before Flying from the Gambler.
This alternate method is sometimes known as the Quick Mew glitch, as it allows the player to obtain Mew at the earliest possible point in the game.
It is very similar to Method #1, except that the Jr. Trainer on Route 24 west of Nugget Bridge should be used in place of the Route 8 Gambler, and the first Swimmer in Cerulean Gym used in place of the Route 25 Youngster. As Fly is not available at this point in the game, the player must catch an Abra and use its Teleport in place of Fly.
At the end of the glitch, the player should return to Route 24 rather than Route 8, as that is the area where the glitch began.
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The reason why the Route 8 Gambler and Route 24 Jr. Trainer can be used to begin the glitch is because they are 'long-range' Trainers; i.e. their vision range is the maximum possible and they will see the player the moment they appear on the screen in the line of sight. When the game draws any NPC on the screen, that NPC is first placed in their default direction (south) for one frame, before being updated to face their correct direction. This allows the start menu to be opened during the one frame that the player is within the Trainer's line of sight but has not yet been seen. The remainder of the steps effectively trick the game into believing that the player is conducting a battle when in fact he/she is not, causing various values to be read improperly and creating the glitch.
The player must battle a Trainer (not just a wild Pokémon) in between the escape and the final encounter, otherwise no encounter will appear. This is because the game initially expects the player to start a Trainer battle (from the 'escaped' Trainer) and the player must 'finish' the battle before the game can begin behaving properly (even if the finished battle is actually a different Trainer). For the same reason, this Trainer must walk up to the player; he/she cannot be talked to directly or walked immediately in front of to initiate the battle, or the game will freeze.
The reason why Mew specifically appears at the end of the glitch is based on the relationship between its index number, which is 21, and the Special stat of the Pokémon last battled. In both of the above cases, the Youngster's level 17 Slowpoke and the Swimmer's level 16 Shellder, the last Pokémon in their respective parties, have a Special stat of 21.
Any method of 'escape' from the long-range Trainer may be used, including Dig and the Escape Rope if the Trainer is in a cave area.
The mechanics of the Mew glitch are rife with possibilities, making it one of the most useful glitches in the game.
Extended Mew glitch
As the Pokémon that appears from the glitch is based on the Special stat of the Pokémon last battled, the player can easily manipulate the wild Pokémon that appears from the glitch by battling a different Trainer or even encounter wild Pokémon right before the encounter. For example, the Lass at the top of the first floor of Mt. Moon has a level 11 Bellsprout with a Special stat of 22 last in her party, and so battling her last in the glitch will result in encountering a level 7 Gyarados, whose index number is 22.
The easiest way to manipulate the last encountered Special stat while performing the glitch is to obtain it on one's own Pokémon, and then battle a Ditto. Send out the Pokémon with the desired Special stat on itself, and wait for the wild Ditto to use Transform. As the move Transform copies all of the target's stats, the Ditto will take on the Special stat of the Pokémon sent out. After defeating it, proceed as normal, being sure to not battle any other Pokémon before the end of the glitch.
The Special stat on the player's own Pokémon can be caused either by natural leveling or by stat experience.
In Pokémon Yellow, as wild Ditto can only be found in the basement of Pokémon Mansion, it is highly recommended to bring an Escape Rope or a Pokémon who knows Dig, in order to leave the Mansion immediately after battling the Ditto. If the player attempts to walk out of the Mansion and encounters another wild Pokémon on the first floor, its Special stat will overwrite that of the Ditto and mess up the glitch.
As it is easily possible for one's Special stat to exceed 190, the highest index number of a valid Pokémon, the Ditto glitch allows easy access to several glitch Pokémon for Special stats of 191 or higher. For example, in Red/Blue, a Special stat of 198 will lead to battling a ゥL ゥM 4. If the Special stat exceeds 200, the player will instead battle a glitch Trainer instead of a wild Pokémon. It is even possible to battle Professor Oak in this way. Some very high Special stats may lead to the memory-corrupting ZZAZZ glitch, and so should be avoided.
Special stats of 256 or higher will wrap around to 0 and continue from there, as index numbers are limited to one byte. For example, a Special stat of 300 will yield exactly the same effects as a Special stat of 44. This is the only way to use the Ditto glitch to encounter Pokémon whose index values are less than 5 (as Special stats cannot normally go lower than that).
List of encounter values
Glitch Trainers are in bold.
A Pokémon encountered at the end of the Mew glitch most commonly appears at level 7. The reason for this is because, just as the previous Pokémon's Special stat corresponds to the index number of the encountered Pokémon, the previous Pokémon's attack stage modifier corresponds to the level of the encountered Pokémon. This attack stage is often expressed as ranging from -6 to +6, but is actually stored internally as a number ranging from 1 to 13, with 7 being the default. Therefore, if the player uses a move like Growl once on the previous Pokémon, the encountered Pokémon will appear at level 6.
Using Growl six times to minimize the attack stage modifier will result in encountering a level 1 Pokémon, which cannot normally be found and can lead to the experience underflow glitch.
If the Ditto glitch is used and a glitch Trainer is encountered, the team that the Trainer class uses corresponds to the attack stage modifier. This usually results in the game attempting to load the 7th possible party of that Trainer, which often does not exist and leads to invalid party data and glitch Pokémon on the Trainer's team. However, if the attack stage modifier is first lowered to 1, then the game will attempt to load a valid 1st party. This is most notable in the case of battling Professor Oak, who has three valid parties (corresponding to each of the starter Pokémon) and so any attack stage modifier from 1 to 3 will work.
Snorlax skip glitch
TODO: Explain, this is a pretty big side effect
Mew glitch without a long-range Trainer
If there is tall grass in the tile immediately in front of a Trainer's line of sight, or a Trainer is in a cave, then the 'Trainer-Fly' effect can be initiated even if that Trainer is not a long-range Trainer. This can only occur if the player is lucky enough to generate a (natural) wild encounter on the exact tile immediately in front of the Trainer. If the player then blacks out from this wild battle, they will be warped back to the Pokémon Center as normal, but the Trainer will see the player before he/she warps back (the "!" is visible extremely briefly during the blackout animation).
A number of glitch items enable the player to move around on the map without being seen by Trainers; if the glitch item's effect is disabled while in front of a Trainer, then a Trainer-Fly effect can begin.
No other Trainers remanining
As the player must battle another Trainer (in a different area) after escaping from the long-range Trainer before the final encounter can appear, this can cause problems if all possible available Trainers have been defeated. The Elite Four can be rebattled indefinitely, but as the A button to talk to characters remains nonfunctional until a Trainer has been defeated, it is not possible to challenge them directly. Nor can the player directly save the game as the start menu cannot be opened. To remedy this:
After escaping the long-range Trainer, the player must visit a PC and save the game indirectly by switching boxes. After saving, the player can reset the game; the Start, A, and B buttons will now be functional. The player can then defeat the entire Elite Four and Champion in place of battling another Trainer (as no such Trainers exist), and finally return to the area of the first long-range Trainer to complete the glitch. It is recommended to flash the start menu right before returning, to prevent a possible text box error (see below).
Text box errors and variations
If the player causes a text box to pop up before returning to the area where the long-range Trainer was escaped from, such as by talking to a NPC or reading a sign, then something other than the start menu will pop up at the end of the glitch. This is typically dialogue from Trainers on the route, which may be followed by a wild Pokémon battle, after which the player will no longer be able to move. Alternately, the text may be from interacting with a sign or an item; in the latter case, the item will appear in the player's inventory and disappear from the route as if they had picked it up normally. This may also allow the player to obtain items which are not currently on the route. Finally, instead of a text box, the player may trigger other glitches, such as glitch songs or 0 ERROR.
In other languages
|| "fifth method"
|| Named after user fifthヽ(´ー｀)ノ◆Fi3PJTZKLQ who posted about it on 2ch. (source)
|| "Special encounter"
|| Named after the fact the last Special in memory determines the encounter. (source) Less common than "fifth法".
- ↑ Nation Master - Encyclopedia: Mew glitch
- ↑ Glitch City Laboratories' page about the Ditto glitch