Pokémon Red / Blue · Game Boy · 1996 · Impact: Beloved
MissingNo — a garbled sprite representing a missing or invalid Pokémon data entry — became one of gaming's most beloved bugs by appearing as a catchable wild Pokémon through the Old Man glitch, duplicating items, and spawning an enormous mythology around its nature and origins.
MissingNo (short for "Missing Number") is not a single bug but a category of invalid Pokémon data entries that the game's encounter system can load under abnormal circumstances. The primary route to encountering MissingNo is the Old Man glitch: the Old Man tutorial in Viridian City temporarily overwrites the player's name in memory with the Old Man's name for display purposes during his fishing demonstration. After the tutorial, the player's name bytes are restored, but if the player immediately uses Fly to reach Cinnabar Island and surfs along its eastern coast — a tile edge where wild encounters are generated from incorrectly loaded zone data — the game reads the player's name characters as Pokémon species IDs. Most characters in the player's name correspond to Pokémon species IDs that exist in the game normally; some correspond to invalid entries that load as MissingNo, a visually glitched sprite with scrambled data. MissingNo's most dramatic property is that encountering it — regardless of whether the player catches it or flees — sets the item count of the sixth inventory slot to 128. Because the game displays item quantities up to 99, the value 128 displays as a question mark, but the items are all present and usable. This turned MissingNo into an item duplication engine: a player who placed a Master Ball, Rare Candy, or other valuable item in the sixth slot could encounter MissingNo to "duplicate" it to 128 copies. The Cinnabar coast encounter became one of the most widely known techniques in the franchise's history, and MissingNo's corrupted sprite — two irregular blocks of noise pixels — became an icon that appeared in fan art, merchandise, and cultural references for decades after the game's release.
Pokémon's wild encounter system generates the species of an encountered Pokémon by reading from a zone-specific encounter table. On Cinnabar Island's eastern coast — a tile row that borders the ocean but belongs to a map zone that has no valid encounter table — the engine reads from whatever data occupies the expected table address. Due to how the game manages temporary name overwrites during the Old Man tutorial, the player's character name bytes remain in a memory location that the eastern coast encounter table address maps to after the tutorial sequence.
Each byte of the player's name is read as a species ID. Standard alphabetic characters have ASCII-adjacent values that correspond to specific Pokémon IDs: the character L, for example, corresponds to species 108 (Lickitung). The character 0, spaces, and certain punctuation produce invalid species IDs that the game loads as MissingNo, the error-state entry. Because the encounter is generated from real name data, the species encountered depends on the player's name — different names produce different Pokémon from the coastal encounters, and players who learned this created specific name strings to target particular species, including Pokémon not normally obtainable in their version of the game.
MissingNo's transition from software error to beloved cultural figure happened through the same mechanisms as gaming mythology generally: playground sharing, magazine documentation, and the absence of official explanation. Nintendo's silence about MissingNo — neither confirming nor denying its nature, offering no official caution, issuing no patch — created a void that player imagination filled. Theories proliferated: MissingNo was a hidden 152nd Pokémon; it was a development placeholder that Nintendo forgot to remove; it was Pikablu (another persistent Pokémon myth) in its true form; it was a test entry for future DLC.
None of these theories were true, but their circulation gave MissingNo a mythological weight that legitimate Pokémon never achieved. The corrupted sprite became recognisable to players who had never personally encountered it, transmitted through descriptions, photographs of Game Boy screens, and eventually internet images. By the time Pokémon Gold and Silver released in 1999, MissingNo was already a franchise institution — a bug so beloved that its absence from later games was treated as a loss by players who had grown up with it. Its legacy continues: the unofficial Pokémon communities that document Generation I glitches treat MissingNo as a central object of study, and its cultural resonance has made it the most documented bug in any single video game franchise.