9. A Secret Dev Message Hidden For 26 Years - Donkey Kong
While the vast majority of Easter eggs are uncovered within mere days, weeks, or maybe months of the game hitting shelves, this sneaky Donkey Kong Easter egg laid dormant for more than a quarter-century before finally being unveiled.
In 2008 Landon Dyer, who programmed the original Donkey Kong port for the Atari 400 and 800, made reference to an Easter egg he coded into his port of the game, though given how much time had passed since its 1983 release, he didn't remember the particulars of its unlocking.
Furthermore, he insisted that it was "totally not worth it." Oh, how right he was.
Gamer Don Hodges soon enough set to uncovering the Easter egg by delving into the game's code, and eventually learned how to unlock the mysterious secret.
Players have to set a new high score of 37,000, 73,000, or 77,000, then deplete all their remaining lives and kill themselves by falling, then set the game difficulty to 4. After doing all this, the player will be greeted at the title screen with the initials "LMD," for Landon M. Dyer.
Again, Landon was totally right about it basically being a waste of time, but you can always count on gamers to enthusiastically find a way to solve even the most hilariously mundane of mysteries.
That it went unchecked for so long however, given how many people have surely sifted through Donkey Kong's code over the years, is impressive.