The Secret of Mew: Why Gen 1's Mythical Pokémon Was Hidden

Summary: Mew, the hidden 151st Pokémon, became a legend through arcade-inspired secrets.Its mysterious origin and connection to Mewtwo helped turn Pokémon from a niche game into a global cultural phenomenon.

Mew has long been the subject of schoolyard rumors and legendary speculation. In this first part, we explore what kind of Pokémon Mew is and we take a look at how Mew was programmed into the game.

The Myth, The Legend - Mew

The Ancestor Of All Pokémon

Mew is a Mythical Pokémon introduced in the first generation of games. At the time, no one knew of its existence. It wasn’t until the May 1996 issue of CoroCoro magazine—two months after the release of Pokémon Red and Green in Japan—that Mew was officially revealed.

In the Pokémon universe, Mew is said to be the ancestor of all Pokémon. It contains the DNA of every species, which is why it can learn almost every move, despite being a Psychic-type. Mew also has the ability to turn invisible and transform into other Pokémon or living creatures. When threatened, it can shield itself inside a glowing orb—as seen in Pokémon Snap for the Nintendo 64.

When players enter the Pokémon Mansion on Cinnabar Island in the first-generation Pokémon games, they can find mysterious diary entries about Mew. According to the entries, it was Mr. Fuji who discovered Mew deep in the jungle and gave it its name. Along with other scientists, he recovered DNA from Mew and used it in an attempt to create a clone. Their goal was to engineer the most powerful Pokémon of all time—Mewtwo.

Because of these similarities, it has been rumored that Ditto is a failed experiment of Mew being cloned. While this theory isn't confirmed in the official games or anime, it has sparked a lot of discussion due to several key similarities between Ditto and Mew. They share the same color scheme, including in their shiny forms, have the same base stats, and are the only Pokémon that can transform. Additionally, Ditto can be found in the Pokémon Mansion on Cinnabar Island, the very place where Mewtwo was created.

Ditto’s strange appearance—its simple, blob-like form with no distinct features—could be seen as a side effect of failed cloning, perhaps a result of the scientists' attempts to replicate Mew’s extraordinary genetic traits. While the official Pokémon lore doesn’t explicitly confirm that Ditto is a failed clone of Mew, this theory makes sense given the striking similarities between the two.

How Arcade Rumors Inspired The Creation Of Mew In Pokémon

The Truth Behind Mew’s Secret Role On Pokémon Red And Green

Shigeki Morimoto - Creator of Mew

There are a lot of stories about how Mew got into the first generation of Pokémon games. One of the most popular rumors is that Shigeki Morimoto secretly programmed Mew into the games. This is more of an urban legend, although some parts of it are true. For that, we have to go back to Satoshi Tajiri's days in the arcade.

Tajiri often skipped school to play at local arcades, where he spent time on games like Xevious and Space Invaders. Both games were rumored to have hidden secrets in their gameplay. In the case of Xevious, it was an F-4 Phantom fighter jet supposedly left in the game’s code. Although it could never actually be seen by players, there was a widespread belief that you could spot it with a one-in-a-million chance. Gaming magazines at the time reported these rumors as fact.

Tajiri took inspiration from this idea when creating Mew—programming a character into Pokémon Red and Green that exists in the game but doesn’t normally appear. It became a secret passed on through word of mouth, feeding the mystery of its existence. But Tajiri wanted Mew to be caught, to become a lasting memory for the player. So while Morimoto did the programming, the idea of hiding Mew came from Satoshi Tajiri—not Shigeki Morimoto.

How 300 Bytes Of Free Space Made All The Difference

Debugging Pokémon Red and Green took a lot of time and effort. In a later interview, Satoshi Tajiri stated that it was the most expensive debugging process in Nintendo’s history. Game Freak wanted to include a Pokémon that could serve as the origin of Mewtwo. Red and Green already had references to this scattered throughout the Pokémon Mansion. However, after debugging was complete, Nintendo instructed Game Freak not to tamper with the game’s code. But when the debug features were removed, about 300 bytes of space were freed up—just enough to add one more Pokémon to the game: Mew.

Morimoto asked Sugimori for the design of Mew. Sugimori created the design for Mewtwo and other Pokémon in the first generation. Unfortunately, Sugimori never found time to design Mew, so Morimoto had to do it himself. With very limited space—only 300 bytes—there was no room for a detailed design, Pokédex entry, or even full stats. Mew’s sprite had to be compact, measuring only 40 by 40 pixels, compared to Mewtwo’s 56 by 56 pixels. There wasn’t enough space to assign Mew a proper color palette either, which is why in Generation I, Mew appears mostly white with a soft pinkish glow. Morimoto also mentioned that, according to the Pokémon lore, Mewtwo was created as a clone of Mew. But in reality, it was the other way around—Mew was actually based on Mewtwo, since Mewtwo had already been created by the time Mew was added to the game.

Mew Encounter Pokémon Blue

The Playground Rumor Of Mew

Game Freak was in on the plan to add Mew to Pokémon Red and Green, but no one informed Nintendo that Mew had been secretly included. Nintendo only found out when players began to encounter a glitch in the game.

Through this glitch, fans discovered a way to encounter a wild Mew—something that wasn’t supposed to happen. When Nintendo first learned about it, they were furious. But once they realized that the glitch was fueling rumors and driving a surge in game sales, their anger quickly faded.

Just like the rumors surrounding Xevious and Space Invaders, the tale of a secret 151st Pokémon spread across Japanese playgrounds like wildfire—exactly as Tajiri had intended.

How Mew Turned Pokémon Into a Global Phenomenon

Thanks to this playground rumor, Pokémon Red and Green shot to the top of the sales charts a year and a half after their release in Japan. That success alone was more than enough reason to localize the games into six languages. The urban legend of Mew played a key role in helping Pokémon become the global franchise it is today. After its massive success in Japan, Pokémon began spreading to other parts of the world. It quickly grew beyond just a video game, expanding into an anime, trading card game, manga, and a wide range of merchandise.

Conclusion

Mew was never meant to be the star of the show—but it became one anyway. What started as a hidden experiment tucked into the final bytes of Pokémon Red and Green evolved into one of the most legendary and talked-about mysteries in gaming history. From secret jungle diaries to glitch-fueled rumors on schoolyards, Mew blurred the line between game and myth. Its presence not only added depth to the Pokémon world but sparked curiosity and excitement that helped propel the franchise to global fame. More than just the 151st Pokémon, Mew became a symbol of mystery, imagination, and the kind of magic that turns a game into a phenomenon. And in many ways, that secret sprite hidden deep in the code may have changed everything.

In Part Two of this series, we dive into the wildest Mew myths, legendary playground rumors—and yes, how you can catch Mew for yourself!