From Bulbapedia, the community-driven Pokémon encyclopedia.
A glitch Pokémon is a Pokémon that only exists in the games due to a programming oversight, when the game attempts to draw up data for an invalid Pokémon.
Some glitch Pokémon have characteristics derived from the game's default error handling capabilities for an invalid Pokémon, such as the name "Missingno." or "??????????". Another example of this is learn-set data for a Generation IV Egg, where it learns Splash as a starting move, likely to prevent the game from freezing due to an invalid move being used.
In Generation I, some glitch Pokémon may freeze the game if sent out on the opponent's side, depending on their Pokédex number and the version used, and glitch Pokémon with index numbers greater than 199 will always bring up equivalent glitch Trainers if encountered directly in the wild. These glitch Pokémon cannot be obtained via a wild battle, and must be obtained using a different glitch to the Ditto glitch or old man glitch, such as evolution from another glitch Pokémon, trading an equivalent index number glitch Pokémon to another version, or the Johto guard glitch.
Additionally, catching certain obtainable glitch Pokémon in Generation I may cause endless Pokédex data to appear. To avoid this, the player must have activated a specific flag, if this is a hybrid glitch Pokémon, the flag is activated by either seeing a specific Pokémon or owning a specific Pokémon. Specific glitches (such as the Super Glitch move) may cause the saved file to be corrupted or erased.
- Main article: List of glitch Pokémon
- There are 39 Missingno. with identifiers in between real Pokémon, which would add up to 190 Pokémon.
- Shigeki Morimoto confirmed that there were once 190 Pokémon planned for development in Pokémon Red and Green. The error handler Missingno. is used for blank or formatted Pokémon data. Many of its characteristics are either a translated 0 value (e.g. default Nidoran♂ cry with pitch 0), or blank data rolled over to the next logical values (e.g. base stats denoting the rosters of several Burglars).
- The reason for the vast amount of glitch Pokémon in Generation I is because only 151 values correspond to valid Pokémon; the final valid index number is Victreebel (0×BE). The species identifier is a single 8-bit (256 values) byte, meaning that there are an additional 105 values including 0 for glitch Pokémon, or 66 values excluding the 39 Missingno. which are located in between the index numbers of valid Pokémon.
- In Generation I, a large number (43) of glitch Pokémon have the small katakana ゥ u in their names. It is unknown as to why this specific katakana character appears so often.
- The only other Japanese character that appears somewhat frequently in glitch Pokémon's names is small ァ a. The hiragana ぉ o and ぇ e also appear, but very rarely.
- The reason for any Japanese text in an English game can be seen here
- Also In Generation I, the most common number in a glitch Pokémon's name is 4, appearing in 23 different glitches.
- 23' 0"/880.6 lbs. are the most common height and weight values for Red and Blue glitch Pokémon, and 23' 2"/1031.6 lbs. for Yellow. It is unknown as to why any glitch Pokémon have the same values, however.