Pokémon Red and Blue/MissingNo.

This is a sub-page of Pokémon Red and Blue.

One of the most popular oddities in Pokémon, and gaming history in general, is the presence of a mysterious, glitchy non-Pokémon called "MissingNo."

Technical Explanations

Known in Japanese as けつばん ("Ketsuban", literally "Missing Number"), this placeholder is used to fill the empty entries in the Pokémon ID list. In the localized versions Red and Blue, there are 39 instances of the string "MissingNo.", each used by an empty entry in the internal index table. However, in the Japanese games 38 of the entries use the name Ketsuban, with the final blank entry instead using the name ゴースト (Ghost) and the Pokémon Tower ghost sprite. As mentioned in the Sprites section below, the graphic is used during the encounter with the ghost in the Pokémon Tower. Despite its graphic being used, this name text isn't normally visible, even during the battle. It's also the only instance of ゴースト (Ghost) in the ROM, as Spirits are always referred to in-game as ゆうれい (Yuurei).

Sprites

Out of all of the instances of MissingNo., 36 of them use interpret garbage data when displaying a sprite, and due to the abnormally large size of this garbled graphic, viewing it causes the player's Hall of Fame data to become corrupted. However, the final three MissingNo. have legitimate sprite data:

Hex	Dec.	Sprite	Purpose
B6	182		Used to display the sprite of the Kabutops fossil in Pewter City's Museum.
B7	183		Used to display the sprite of the Aerodactyl fossil in Pewter City's Museum.
B8	184		Used to display wild Pokémon in the Pokémon Tower before obtaining the Silph Scope.

Cries

Of all of the MissingNo, 30 have cries whose base, pitch, and length are set to 0:

Hex	Dec.	Cry	Base Type	Base	Pitch	Length
-	-		Nidoran♂	0	0	0

Two entries, meanwhile, share their cries with existing Pokémon, respectively Zubat and Dragonair:

Hex	Dec.	Cry	Base Type	Base	Pitch	Length
45	69		Squirtle	29	224	128
89	137		Bulbasaur	15	64	128

The remaining seven entries have unique cries which are not used by any other Pokémon:

Hex	Dec.	Cry	Base Type	Base	Pitch	Length
43	67		Nidoran♂	0	128	16
4F	79		Rattata	34	255	64
51	81		Pidgey	14	224	96
5E	94		Bulbasaur	15	64	192
5F	95		Bulbasaur	15	32	192
7F	127		Rhydon	17	32	16
B5	181		Squirtle	29	0	128

For more information on Pokémon cries, see the corresponding Notes page.

(Source: IIMarckus - Pokémon Cry Data)

Base Stats

Each MissingNo. is numbered #000 in the Pokédex, and since a Pokémon's base stats are ordered by Pokédex number rather than internal index number this results in all 39 MissingNo. sharing the same basic information, including types, stats, moves, and Pokédex data. However, none of this data is actually valid, as the game is actually reading data far beyond the boundaries of the base stats table, misinterpreting data used to define the parties of trainers as base stats.

Pokédex Entry

The Pokédex entry for MissingNo. defines it as a "??? Pokémon" with a height of 1.0m (3.3 ft), a weight of 10.0kg (22.1 lb), and a placeholder Pokédex entry reading 「コメント さくせいちゅう」 ("Comment under construction"). However, this information was not translated or localized in the English versions of the games and became garbled, resulting in the Pokédex entry displaying a height of 10.0 ft (3.1m) and a weight of 3,507.2 lb (1,590.8kg).

MissingNo. List

As mentioned previously, only the last three MissingNo. have actual sprite data, though, interestingly, a 2020 Pokémon Blue source code leak revealed the back sprite that was once assigned to most of the entries. More information here.

Hex	Dec.	Front Sprite	Back Sprite	Cry	Unique?
1F	031
20	032
32	050
34	052
38	056
3D	061
3E	062
3F	063
43	067				✓
44	068
45	069				✓
4F	079				✓
50	080
51	081				✓
56	086
57	087
5E	094				✓
5F	095				✓
73	115		-
79	121		-
7A	122
7F	127				✓
86	134
87	135		-
89	137				✓
8C	140
92	146
9C	156
9F	159
A0	160
A1	161
A2	162
AC	172
AE	174
AF	175
B5	181				✓
B6	182		-
B7	183		-
B8	184		-

Encountering MissingNo.

Method

In the English Red and Blue versions, the best-known way to find yourself face-to-face with a MissingNo. is to follow these steps:

• Travel to Viridian City, then talk to the old man who shows you how to catch Pokémon and accept to watch his demonstration.
• Once the tutorial is over, immediately use Fly to travel to Cinnabar Island or surf to Seafoam Islands (water route encounters will not overwrite land encounter data if there is no tall grass on the same route).
• Once there, surf up and down the east coast of the island on the tiles where the water borders the land. Depending on the name you chose for your player character, an assortment of Pokémon and trainers at varying levels will appear.
• If you used one of the game's preset names, or input a custom name that included the characters G, H, J, M, S, :, ], a, b, c, m, o, p, v, w, x, or y, you may find yourself battling a MissingNo.

Explanation

The reasons for this curiosity are twofold:

First off, land/water border tiles are normally programmed to function like water tiles, and thus generate encounters with wild water Pokémon. However, the land/water border tiles on Cinnabar Island are unusual in that they behave like grass tiles. This means they attempt to generate encounters from the wild Pokémon encounter table, a list of Pokémon defined for each map. This table is normally repopulated each time a player enters an area containing wild Pokémon. However, because Cinnabar Island has no Pokémon encounter data, entering the map doesn't cause the table to update. As such, encounter data from the player's previous location remains in memory without being overwritten.

Secondly, during the Pokémon-catching demonstration in Viridian City, the player's name is changed to "OLD MAN". In order to preserve the player's moniker, their original name is stored into the wild Pokémon encounter table for the duration of the battle, then copied back over once the demo ends. As soon as the player enters an area with wild Pokémon encounters, this table will be repopulated, so this little programming sleight-of-hand normally has no effect on the game.

The combination of these two quirks is where things start to fall apart. Because Cinnabar lacks encounter data, entering the map does not cause the encounter table to repopulate. As a result, flying directly from Viridian to Cinnabar after watching the old man's demonstration results in the player's name remaining in the encounter table. The characters that make up the player's name are thus treated as encounter data, but these don't always correspond to valid Pokémon IDs. As the battles triggered by surfing up and down the coast of Cinnabar Island are drawn from this table, the player can, accordingly, expect to encounter anything from rare or legendary Pokémon to MissingNo., 'M, and glitched Trainers at impossibly high levels.

For a full list of which characters generate which encounters, refer to this chart on Bulbapedia.

Side-Effects

Hall of Fame Corruption
A well-known consequence of encountering MissingNo. in battle is the corruption of the Hall of Fame data in the player's PC. The reason for this corruption is that the games use SRAM as temporary storage when decompressing sprites. MissingNo.'s garbage data is interpreted as a compressed picture, resulting in an extraordinarily large sprite that extends beyond the bounds of the sprite decompression buffer, overflowing into the Hall of Fame data that follows it, and overwriting some of the data there (the size of MissingNo.'s sprite is also the reason for wild MissingNo. encounter taking an abnormally long time to load).

On a side note, what follows the Hall of Fame data is the sound engine data. In Red and Blue, MissingNo.'s sprite data isn't large enough to extend into it. In Yellow, however, it is, resulting in the sound engine data being interpreted as a Pokémon cry, and thus causing an unholy shriek as the battle begins.

(Source: YamaArashi & Sanqui)

Item Duplication
One of the contributors to MissingNo.'s fame is the item duplication glitch: Any time the player encounters MissingNo., 'M, or another glitch Pokémon with Pokédex number 000, the game attempts to set the "Pokémon has been seen" flag for that number in the Pokédex. Due to an integer underflow when calculating the address of this flag, the game instead sets the highest bit of the quantity of the sixth item in the player's bag, which results in a 128 unit increase.

If you catch the 'mon, the sixth item duplicates again (assuming it's been reduced to less than 128).

Other Versions

This glitch is not present in Japanese Red, Green, and Blue, as no Pokémon encounters occur on the land/water border tiles. Meanwhile, this glitch was also fixed in the Spanish and Italian versions of Red and Blue by programming the border tiles to behave as water tiles. However, it still remains in the German and French versions of these games, though in the French version encountering either MissingNo. or 'M causes the game to freeze.

The glitch was removed in all versions of Yellow by blanking the encounter table before overwriting it, and programming the border tiles to avoid triggering Pokémon encounters, as was already the case in the Japanese games.

'M

The glitch Pokémon 'M (whose name consists of corrupted graphics with "'M" in the middle) is often confused with MissingNo., as both can be encountered using the Old Man glitch, and both share the Pokédex number 000. However, unlike MissingNo., 'M's game statistics are made up of garbage data, which is not actually pulled from unused internal index entries. Its similarities to MissingNo. are mostly a result of sharing the same Pokédex number. However, it also has the ability to evolve into Kangaskhan and learn the move Pound.