Perhaps the most well hidden Easter Egg appearing on this list, I’m not sure anyone would have even noticed the three letters that could appear on Donkey Kong’s title screen even if they met the parameters accidentally. Of course those parameters are ridiculous anyhow: set a specific high score, die by falling, set the difficulty to 4 back at the title screen, and let the intro loop play.
What was so secret that such a complex method of discovery was needed? What could possibly need to be hidden for 26 years before someone finally found it, and only then after the developer tipped us off to its existence in a blog post? The developer’s initials, LMD, which will appear at the bottom of the title screen. That’s it. I don’t mind the initials, if I had the chance to hide my initials in a game I’d totally do it, but the work it takes to see them is just crazy. No wonder it took 26 years.