Mew was secretly programmed into the first generation of Pokemon games just two weeks before the final cartridges were manufactured, completely bypassing Nintendo's strict quality assurance testing.

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Mew was secretly programmed into the first generation of Pokemon games just two weeks before the final cartridges were manufactured, completely bypassing Nintendo's strict quality assurance testing. Programmer Shigeki Morimoto noticed there was exactly 300 bytes of free space left on the cartridge after they removed the debugging tools, so he quietly slipped the mythical monster in as a personal prank. Nintendo management had absolutely no idea the creature existed until players started stumbling across it through random glitches and playground rumors began spreading like wildfire. The accidental mystery ended up generating massive hype for the game, rewarding an act of rogue programming insubordination that would absolutely get a developer fired and sued into oblivion in today's corporate climate