MissingNo. (Japanese: けつばん Ketsuban) is a name shared by several glitch Pokémon in Pokémon Red, Blue, and also Yellow. The name is most commonly used to refer to a Normal/ -type glitch Pokémon whose sprite consists of corrupted data or a Normal/999 in Pokémon Yellow. It is arguably the most well-known glitch Pokémon in the game series.
In the early Pokémon video games, the programmers had to use variables to refer to different Pokémon by number. Variable sizes must be powers of two. The smallest variable they were able to use was the size of one byte—that is, capable of holding any value from 0 to 255 with zero counting as a slot. (The next smallest size could only hold 0 to 127, which would not have been enough for all 151 Pokémon.) Because there are only 151 legitimate Pokémon in Generation I, this left 105 slots unoccupied. 37% of these are occupied by empty slots named Missingno., 53% are trainers (this is the reason why "wild" trainers are sometimes found on the coastline of Cinnabar Island), and the rest are other glitch Pokémon.
Unlike most glitch Pokémon, whose names consist of data cobbled together from random locations, Missingno.'s name is clearly a deliberately-added abbreviation of "missing number". This is because "Missingno." was added as a name for the empty slots to avoid the game crashing if a glitch Pokémon was encountered.
The Missingno. most commonly encountered during glitches is a Normal/Bird-type Pokémon, whose sprite is a backwards letter "L"-shaped chunk of "fuzz". Bird is a beta type that was deleted from the game; it functions identically to Normal. The sprite results from the game treating non-graphical data as an image. This form of Missingno. almost always knows Sky Attack and Water Gun; of particular note is the fact that it knows two Water Guns. The fossil and ghost sprite Missingno.s have the same moveset as the most recently viewed Pokémon. You can get it in the Red, Blue, and Yellow versions, though in Yellow, Missingno. was encountered a different way. Missingno.'s stats will change depending on the player character's last party Pokémon.
Other forms of Missingno. use the fossilized Aerodactyl and Kabutops sprites from the Pewter City museum. The fourth form uses the sprite shown when one encounters a Ghost Pokémon in the Pokemon Tower without having the Silph Scope. These are actually separate glitch Pokémon that share a name; they can be distinguished both by their sprite and by their differing characteristics. "Fuzz" Missingno., for example, uses a fixed moveset, whereas the fossil and ghost Missingno.s' moves change depending on the last Pokémon in one's party (among other things). The fossil MISSINGNO.s also tend to turn into RHYDON upon capture, if a player character hasn't yet viewed their (empty) Pokédex entries (by, of course, capturing them).
Though they are all distinct, all known Missingno. forms have several properties in common. They all share the Pokédex number 000. Encountering Missingno. will increase the quantity of the sixth item in a player character's inventory to above 128. (This is because the bit used to keep track of whether MISSINGNO. has been caught is also part of the byte used to track the quantity of the sixth item in a player character's inventory.)
The sprite MISSINGNO.s use in the party screen is composed of random 8-by-8-pixel tiles shown on-screen. This means that it is often composed of chunks of terrain and NPCs. Viewing a MISSINGNO.'s stats screen causes a similar scrambling effect: most, if not all, all in-battle Pokémon and Trainer sprites become scrambled. Viewing the stats of a normal Pokémon fixes the problem, or if MISSINGNO.'s level goes to 100 it will also fix but if you look at MISSINGNO.'s stats it will revert.
MISSINGNO. does not evolve into any Pokémon. However, a different glitch Pokémon with a similar sprite and properties, but different name ('M) does evolve into the Pokémon Kangaskhan.
Contrary to popular belief, MISSINGNO. does not appear in any game outside of the Generation I games. However, similar Pokemon known as ????? (Generation II), ?????????? (Generation III), and DPBox (Generations IV and V), which look slightly similar and fill similar roles, appear in successive games.
Encountering Old MISSINGNO.
There is a glitch (called the "Old Man trick") in Red, Green (Japan),and Blue that allows a player character to battle nearly any Pokémon they wish, depending on the characters of their name. The player character should start by viewing the Old Man's Pokémon catching tutorial in Viridian City. Immediately afterward, the player character should Fly to Cinnabar Island and Surf on the east coast (the half-land half-sea tiles). They should not, at any point, swim onto a fully-water tile. Depending on the characters in the player character's name, they may eventually encounter MISSINGNO.
This glitch works because of a programming oversight. When the Old Man's tutorial is displayed, the game needs to change the player character's name to "OLD MAN", so that the in-game dialogue states that "OLD MAN threw a Poké Ball!". However, it would be rather unfortunate if the player character's chosen name was permanently changed to "OLD MAN". Such a scenario is easily avoided, however; the game simply copies the player character's chosen name to an area in memory that is not currently being used. After the tutorial, the name is copied back, replacing "OLD MAN".
Unfortunately, Game Boys do not possess a lot of free memory. In an effort to make the most of all available RAM, the game copies the player character's name into the space used to keep track of what wild Pokémon can be seen in the current location. The programmers reasoned that such an action normally wouldn't cause any glitches because the correct data for wild Pokémon available is written to this area in memory whenever the player character travels to an area where it is possible to catch wild Pokémon.
There was one critical mistake that the developers made, however. The Cinnabar Island map, like the maps of all cities in the game, does not contain any wild Pokémon data. However, the east coast tiles were coded to trigger wild Pokémon battles. The effect is that when the player character travels from a city to Cinnabar Island directly, the wild Pokémon list is not rebuilt. This means that when sailing on Cinnabar's east coast, the player character will encounter whatever wild Pokémon were available at the last area they were traveling in. (This is a useful trick for catching Safari Zone Pokémon; after exiting the Zone, fly immediately to Cinnabar and Surf on the east coast. You'll be able to battle Kangaskhans and the like on your own terms.)
However, when performing the Old Man Trick, the wild Pokémon data holds the player character's name, rather than the wild Pokémon available at the last location the player character explored. When a wild battle occurs on Cinnabar's east coast, the game will read the player character's name as wild Pokémon. The effect is that the text characters in the player character's name will determine the species and levels of wild Pokémon on the coast. Not all available text characters correspond to normal Pokémon, meaning that this glitch may be used to encounter glitch Pokémon, MISSINGNO., included. Another thing to note is that most legitimate Pokemon can be encountered with this method, including Mewtwo, and even some "wild" Trainers that have glitched parties and may crash your game. Hunting these without experience with glitch Pokemon is inadvised.
This effect is relatively easy to exploit. The species are controlled by the third, fifth, and seventh characters of the player character's name. The second, fourth, and sixth characters of the player character's name determine the levels of wild Pokémon encountered via the Old Man Trick. The characters "w", "x", and "y" will yield the Kabutops, Aerodactyl, and Ghost forms of MISSINGNO., respectively. If the graphics start to scramble, look at one of your Pokemon's Pokédex entries. The gameplay should perform normally.
MISSINGNO. can also encountered by using a cheating device.
- MISSINGNO.'s Japanese name (けつばん Ketsuban) means "missing number".
- MISSINGNO. is the most well-known glitch Pokémon.
- MISSINGNO. and 'M are the only glitch Pokémon to have Normal as a secondary type.
- MISSINGNO. is known to scramble Hall of Fame data.
- MISSINGNO. is the only Pokémon to know the same move (Water Gun) twice, if Smeargle learning Sketch doesn't count.
- MISSINGNO. only appears in Generation I. Similar Pokémon appear in other games, see above.
- MISSINGNO. in Pokémon Yellow is a Bird and Normal dual type.
- Supposedly, if the player character eventually catches MissingNo., the save file has a minimal chance to be compromised and deleted, since Missingno. is not supposed to exist, but this is a hoax.
- Occasionally Missingno will transform into another Pokémon after catching it.