Warning: This article contains references to the plot of Pokémon: Red and Blue and the more recent (but related to the topic here) game, Doki Doki Literature Club.

In my flowery ring binder ofandcheats, there was one set of instructions that spoke to my eight-year-old self most of all. I'd heard from friends (and many, many GeoCities pages ) that 'the MissingNo cheat' could destroy your game—but it could also get you unlimited Rare Candy. This seemed like a fair trade to me.

The first Pokémon games for the Game Boy included 151 Pokémon (including the ultra-rare Mew, if your parents were long-suffering enough to drive you to one of the Nintendo promo events where it was distributed). But by following a seemingly random series of steps, players could encounter a 152nd Pokémon, MissingNo (Missing Number), which took the form of an L-shaped block of pixels.

The utter strangeness of MissingNo fascinated me, my childhood friends, and a bunch of other kids on the Internet at the time. But what I didn’t know then was that it would eventually also catch the interest of sociologists, who were intrigued by the mythology players had created around the Pokémon and the way that the glitch changed our relationship to the games.

Finding a missing number

In her 2007 paper Creative Uses of Software Errors: Glitches and Cheats (co-authored with her father, William Bainbridge of the National Science Foundation), Wilma Bainbridge called MissingNo “one of the most popular glitches ever in game history.” Bainbridge believes that it helped to inspire the widespread interest in glitch hunting and speedrunning (completing games as fast as possible, often with the help of glitches and cheats) that we see today.

“Just by MissingNo being such a large glitch, it really got people interested in looking for glitches in general,” Bainbridge, now a post-doctoral fellow at the National Institute of Mental Health, tells Ars. “Pokémon also came out right when the Internet was starting to become mainstream and when it was starting to get faster. So this was one of the first glitches that really disseminated quickly.”

Encountering MissingNo in these games allowed players to duplicate their items, including items that boost Pokémon’s stats. But there were risks—the glitch would also permanently corrupt players’ Hall of Fame data and, if it was caught and used in battle, it could make graphics appear glitchy. Rumors abounded that MissingNo could cause permanent damage to the game or save file, but these were unfounded, in retrospect.

In Red and Blue, the most common method used to encounter MissingNo was what fans dubbed the "old man glitch." This required the player to talk to a man in Viridian City who showed them how to catch a Pokémon, then fly to Cinnabar Island and surf up and down the island’s east coast. Here, players would encounter MissingNo as well as other Pokémon that somehow had levels over the maximum of 100.

When she wrote her paper, Bainbridge thought that MissingNo was a test Pokémon left behind by developers, but she says now that the glitch was the result of a programming error.

“When you enter an area, there's a roster of what Pokémon appear in that area in the memory of the game,” she explains. “There's this very specific strip of [Cinnabar] island, where if you surf up and down on the right side, it seems like they accidentally didn’t code it as water but they coded it as a part of Cinnabar Island.”

When the player surfs on this part of the island, which was mistakenly created without a Pokémon roster, it defaults to the roster of the previous place you visited. When performing the old man glitch, the player has come straight from his tutorial, which uses a sort of dummy roster data based around the player’s name. Because of this, players can encounter many different additional glitch Pokémon (including MissingNo), depending on the letters in their name.

Who knows how Charizard M merging glitch works?

I have no idea what I did, but I accidentally my Charmeleon pic.twitter.com/zkACqhEgqt — Verlis 🎃 (@Verliswolf) June 24, 2018

One such glitch Pokémon was the unique horror that is "Charizard M." This altered version of your favorite fire-breather could prevent you from using the Pokémon Center, turn your other Pokémon into Charizard M copies, and, if stored in the computer box, create an "unstable hybrid Pokémon" (which is not as cool as it sounds).

In my case, the game graphics became so glitched that my character could no longer walk anywhere, so I gave the cartridge to my older brother’s friend who promised to “sort it out” for me. His fix, it turned out, was deleting my entire save file. The memory still stings.