Paul, the Netherlands

Mew
Back when I was a young, avid player of Pokémon Yellow, a rumor spread among my friends and classmates of a Pokémon that there was a hidden mythical Pokémon to be found underneath a truck by the docks – Mew was its name. These stories made the younger me incredibly curious, and I went out to look for the Mew under the truck, but there was nothing to be found.. But there were still kids who did have Mew, so how did they get it? Did they find the secret of Mew? Or did they perhaps simply cheat? This has always been a mystery to the younger me, though now I have found my own ways to acquire the coveted Mew..

Missingno
Another Pokémon-related rumor spread among my friends and classmates as well. There was this ‘Pokémon’ called Missingno, that could destroy your game and delete all of your Pokémon. An older kid who lived nearby told me about it, and about what it could do to your Pokémon, and the thought of that kept me awake at night.. Another kid from my sports team told me that it looks like a weird scratch in your game, and that it would make your own Pokémon look weird too. He told me there were different kinds of Missingno, some were good and gave you items, while others could destroy your game. I never dared to investigate..

MissingNo. (Japanese: けつばん Ketsuban, lit. "missing number"), as it is displayed in-game due to the ten-character limit in Western Generation I games, is a dual-type Bird/Normal glitch Pokémon in Pokémon Red and Blue, and a dual-type Normal/randomly named glitch type (which often has '9' in it) glitch Pokémon in Pokémon Yellow. It is arguably the best known glitch Pokémon, closely followed by 'M (00), and it is the easiest glitch Pokémon to find in the localizations. It has five distinct forms, but the most frequent forms (the Red/Blue and Yellow normal forms) share 36 index numbers each.

In later generations, other glitch Pokémon are sometimes referred to as "a MissingNo.", such as ??????????, ?, and -----. Despite this, the name "MissingNo." is a misnomer in this case; they have little relation to the one found in Pokémon Red and Blue or Yellow.

MissingNo.'s cry is generally the game's equivalent of a "blank" cry: a Nidoran♂ (base 00)'s cry with a pitch of 0 and no echo. This is because the cries of these Pokémon are undefined in the data structure. A few MissingNo. have different cries (specifically 0x43, 0x45, 0x4F, 0x51, 0x5E, 0x5F, 0x7F, and 0xB5). The fact that these cries are valid and not garbage data (i.e. unrelated data read in the wrong way, as is the case with most of MissingNo.'s properties) supports the view that MissingNo. may have originally been a Pokémon that was deleted from the games. (See this section for further details).

The Pokédex entries of MissingNo. and all glitch Pokémon with a Pokédex number of 0 will only appear upon capture if the player has not encountered Cubone, but as with all glitch Pokédex entries, they normally remain inaccessible through the actual Pokédex. An exception to this rule is in Red and Green, where MissingNo. can be "registered" in the Pokédex if the player enables the 'seen' flag for #152 through select glitches and memory corruption. If MissingNo.'s Pokédex data is viewed, Rhydon's cry will be heard, followed by MissingNo.'s (blank) entry and a series of glitchy sounds.

No MissingNo. can evolve or learn any moves through leveling up.

If the RB MissingNo. is traded to Generation II, it will hold a Carbos.