Partially unused and glitched

Partially unused is a side effect of how data in the Pokémon games is retrieved. Functions that retrieve data may simultaneously load valid but unused data leftover from development, as well as glitch data which was never intended to be added there.

Examples

• The MissingNo. before index number 191 have some leftover unused but valid data.
  • Nine of them have some unused cry data.
  • There 39 entries in between the 151 existing Pokémon, adding these together is 190 Pokémon; a former total of Pokémon in leaked source code of Pokémon Blue. Some of the MissingNo. were once these Pokémon, such as Gorochu (index number 175) before they were removed and their data was corrupted. However, three MissingNo. (182, 183, 184) had some data repurposed for the Kabutops Fossil, Aerodactyl Fossil and Ghost front sprites. In the Pewter Museum, internally the game actually loads the Fossil MissingNo. index number to retrieve its front sprite.
  • The names "MISSINGNO." (けつばん) itself (and ゴースト for index number 184 (Ghost) in the Japanese versions (not to be confused with ゆうれい, the final term for Pokémon Tower ghosts)) were intentionally hard-coded into the game. This contrasts with the other glitch Pokémon such as 'M (00) which have their names as unrelated data in the game extrapolated beyond the names table.
  • All MissingNo. Pokédex numbers were to set 000, and in Japanese Pokémon Blue, MissingNo. were given the placeholder Pokédex entry "コメント さくせいちゅう" (meaning 'comment to be written') and became the ??? species. This was not translated, resulting in a glitched Pokédex entry in the localized Pokémon Red and Blue and the corruption of MissingNo.'s original height and weight (1.0 m (3.3 ft) and 10.0 kg (22.1 lb), respectively), showing instead a height of 10.0 ft (3.1 m) and a weight of 3507.2 lb (1590.8 kg).
  • No MissingNo. can learn any moves by level-up or evolve (unlike the other glitch Pokémon).
  • Note while trading MissingNo. to Pokémon Gold, Silver and Crystal results in specific Generation II Pokémon, contrary to popular belief they may not have been intentionally defined as those Pokémon.
• Some partially unused glitch maps, such as Map 0x0B (actual unused data include potential placeholder data (such as the music for map 0x0B matching Viridian City), the unused Fly flag for going to map 0x0B, the hidden Max Elixer in unused but glitched map 0x6F).
• Many things that retrieve placeholder data in general, such as ?????????? and the function to make its sprite a "?" in a circle, ? (glitch Pokémon)'s sprite; in those cases they are commonly forced as glitch Pokémon so bring some invalid data with them (such as base stats for the ones with index numbers other than 0 and 252-276/very high index number glitch Pokémon, possibly - (glitch Pokémon)'s base stats and types are glitched and were never intentionally programmed).