Based on: The miserable, filthy thrill of cheating like an utter and complete bastard.
Like all video game systems, the Game Boy was no stranger to an array of first- and third-party peripherals. Some were good, such as the Game Boy Camera, and some were so, so bad -- remember those bulky Game Boy screen magnifiers? One peripheral, however, had a tremendous impact far greater than its creators ever could have imagined.
The GameShark was a passthrough device that allowed players to input unsanctioned cheat codes into their games and discover secrets accordingly. Essentially, the device detected specific values in the game cartridge and deciphered their meaning. Once that was known, the developers could modify these values and release the codes to people who bought their device. This is why so many of the common codes include numerical-modifying options like extra lives, extra ammo, and so on. While inputting pre-established codes was fun, a whole different joy came from deciphering how the letters and numbers of codes corresponded to the in-game world yourself; industrious players devised their own unique combos to unlock all kinds of weird glitches.
While the GameShark idea wasn’t exactly a novel one—the Game Genie had contentiously performed the same function on the NES years before—the release of Pokémon Red and Blue in 1998 caused the cheat device to take on an entirely new significance. Gone were the days of novelty bonuses that weren’t worth the time taken to input the code. Now, the GameShark could actually advance your standing in the world of Pokémon significantly. By simply inputting a code, you could fight (and thus capture) any pokémon in the game. This included the super-rare ones that you are only supposed to fight once—or in the case of Mew, ones you weren’t supposed to encounter at all. You could max out your party’s stats, access rare items, and even get infinite in-game money. While it may have broken the game in some senses—schoolyard link-battles became either landslide victories or teams of level-100s duking it out—those lucky kids with GameSharks were kings because they had the power to endow anyone with power beyond imagining.
So why all this hoopla over the GameShark’s effect on one game? I think we all know what Pokémon became once it hit, and the significance of a cheat device that drastically warped the playfield for its followers simply can’t be understated. For a while, the Game Boy's definitive title was Tetris, but Pokémon eclipsed it. During the late '90s, the Game Boy was Pokémon. To have free reign in a game that was exclusively about collecting and improving that collection -- a game that had so much of the game-playing audience’s attention -- is truly what made the GameShark a pivotal peripheral for the Game Boy.