MissingNo.

MissingNo. (けつばん "Ketsuban" in Japanese, literally meaning "missing number") is a glitch caused by a bad index number for a Pokémon species. The glitch is found in the first generation Pokémon video games. It is one of the most well-known glitches in video games.

Nintendo confirmed the existence of the glitch and warned players that it could corrupt save files, although MissingNo. is generally safe in most cases of encountering the glitch.

A similar Pokémon known as 'M also exists; it has the same sprite and very similar (but not identical) base stats. Like MissingNo., it is harmless in most cases, but will freeze the game if it's Level 0 and being withdrawn from the PC.

Triggering the MissingNo. Glitch

 * 1) Talk to a man found in the northern part of Viridian City. He will teach the player how to catch a Pokémon.
 * 2) Fly to Cinnabar Island.
 * 3) Surf on the eastern coast of the island.
 * 4) While using Surf, move around, and the player may encounter MissingNo., depending on their name.

Effects

 * A captured MissingNo. should have the Pokédex number 000. Other appearances may have different index numbers.
 * Encountering MissingNo. in battle causes the number of items in the sixth slot of the Bag to increase by 128.
 * Encountering MissingNo. can modify the save game data by corrupting Hall of Fame data.
 * When MissingNo. is encountered in Pokémon Yellow, if a video game crash does not occur, it plays a very, very long cry before displaying the text "Wild MISSINGNO. appeared!"
 * When viewed in Pokémon Stadium, MissingNo. will appear as a substitute doll (as will various other glitch Pokémon).
 * Transferring it to Pokemon Gold/Silver/Crystal will transform them to valid Pokemon, depending on which one you transferred (some of them aren't tradable). Leveling up one will revert them back to Level 1. Transferring them to G/S/C is tricky however,as it requires an exploit called Time Capsule exploit.Otherwise the game will detect the irregularity and abort the trade.
 * When transferring a MissingNo. from the Virtual Console versions of the games to Pokémon Bank, it will shift the names of every Pokémon ahead of it backwards. MissingNo. itself won't be in the Transporter Box, however.

The effects between the international and Japanese versions of Pokémon games vary. Transferring MissingNo. to another game by any means can lead to unexpected results.

Official Nintendo Statement
Nintendo has an official description of MissingNo. listed in their Customer Service troubleshooting section:

"MissingNO is a programming quirk, and not a real part of the game. When you get this, your game can perform strangely, and the graphics will often become scrambled. The MissingNO Pokémon is most often found after you perform the Fight Safari Zone Pokémon trick.

To fix the scrambled graphics, try releasing the MissingNo Pokémon. If the problem persists, the only solution is to re-start your game. This means erasing your current game and starting a brand new one."

Reaction
MissingNo. inspired a lot of memes in Internet culture, including making fun of the glitch. Fans have attempted to rationalize and incorporate MissingNo. as part of the games' canon as an actual in-game character, and sociologists have studied its impact on both players and gaming culture as a whole.

MissingNo. appeared in the May 1999 issue of the Nintendo Power magazine. Despite claims that it could erase save game data, MissingNo. is mostly safe.

MissingNo. is sometimes used as a general term for every glitch Pokémon, but this is a misnomer, as not all glitch Pokémon are called MissingNo., and MissingNo. is a placeholder name rather than an error handler per se.

Sociologist William Sims Bainbridge stated that Game Freak created "one of the most popular glitches ever in game history" and cited its creative usage by players.

Virtual Console re-releases did not patch the glitch for consistency.

Trivia

 * MissingNo. occupies 39 hexadecimal slots out of the 255, found in-between those of valid Pokémon.
 * MissingNo. has the following index numbers: 31, 32, 50, 52, 56, 61, 62, 63, 67, 68, 69, 79, 80, 81, 86, 87, 94, 95, 115, 121, 122, 127, 134, 135, 137, 140, 146, 156, 159, 160, 161, 162, 172, 174, 175, 181, 182, 183, and 184.
 * There were originally intended to be 190 Pokémon compared to the 151 that made it into the final game; this equals 39 Pokémon that were cut and possibly those 39 pokemon are added to gen 2.
 * Three MissingNo. in Red and Blue have different sprites: One is the Ghost from the Pokémon Tower, another is Kabutops' skeleton, and the remaining one is Aerodactyl's skeleton.

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