#4. Arkham City Plans (Arkham Asylum, various)
In a game that sold two million copies within just a few weeks on shelves, you wouldn't think any secret could stay secret for long. But the developers of Batman: Arkham Asylum inserted a secret room that went undiscovered for six months before they finally just came out and announced it themselves.
Six months might not sound like long, but keep in mind that was a period when everyone online who liked Batman or video games--i.e. everyone--was playing. It didn't help that it involved blowing open a completely random, unmarked section of wall with absolutely nothing in the way of hints to point you that direction.
Eidos' marketing team slowly went insane as their incredible viral marketing stunt went undiscovered (the secret room promoted the game's sequel, Arkham City) and eventually just phoned a game site and told them how to do it.
Batman surveys yet another horrifying plan that will torture thousands and he won't just kill the psychopath instead.
If you want to find the secret room (ie the Warden's Secret Office), here's a video showing you how.
#3. The Citadel (GoldenEye, N64)
The opening level of GoldenEye has a secret island. If you only played the game without cheating (that is, without a device like a GameShark), you've never been there.
At the end of the dam level (that is, the first level), there are two directions: Left, leaping into one of the best Bond shots ever, to kill an entire chemical weapons facility full of Russians like a high-explosive aerodynamic ass of badness, or right, to stare across the endless expanse of gray. You find the egg by choosing the second option. Look out there with a scope and you can see a tiny island way out in the distance, and no apparent way to get there.
With a GameShark you can turn on "noclip" mode and that will let you just walk out across the water, off to the undiscovered country.
What you find looks badass, what with the huge turret and gatling gun:
Sadly, looking badass is all it does. What you've found is a half-formed idea the programmers had. The "Citadel" was meant to be an extra part of the level, but as the deadline approached, a combination of lack of memory, lack of time and the realization that they'd already made the best console shooter yet to exist meant there were cuts. Rather than deleting the island, they just deleted the boat that was meant to take you there, wrongly assuming that gamers would be too distracted by all the awesomely shooting people to notice the island.
#2. Developer's Initials (Donkey Kong, Atari 400)
This one is amazing, not because of what the Easter egg was, but because of how ridiculously long it stayed hidden: 26 years.
Back when companies kept programmers in cages and "getting a chair" counted as a promotion, Landon M. Dyer was hired to convert Donkey Kong for the Atari 400. They had the license, the original game was setting arcades aflame across the nation and ... well, that's all. His first task was spending a stack of his own quarters to find out what kind of Kong a Donkey was anyway.
He spent the next five months single-handedly reinventing the game on inferior hardware and ended up so deep in the Matrix that he snapped and hid his own initials in the code.
We're rather afraid that's it
And when we say "hid," we mean they were buried so deep the secret stayed hidden for a quarter century. And even then it was only found because Landon told everyone about it, though he'd forgotten how to unlock it himself.
Seriously. Just this.
Well, one man did it. All it took was for him to pry apart all 25,000 lines of assembly code, backtracking from an AND statement through the insane combination of setting a high score with 37, 73 or 77 as the fifth and fourth digits, losing all his lives--the final death by falling--then resetting the machine to difficulty level 4 and waiting. By that point you're so deeply involved in the game you've legally married it.
But hey, Easter eggs aren't about the destination, they're about the journey. Or something.
#1. Kill Your Friend (Duck Hunt, NES)
You can play as the duck in Duck Hunt.
Now, depending on what type of person you are, or what type of person you were in 1985, you'll either respond by saying, "Well duh, it's mentioned in the manual" or with the much more common, "I PLAYED THAT GAME FOR 10 YEARS HOW DID I NEVER KNOW THAT?!".
Hey, this is a game about holding a gun and killing things, so it's for men, and instruction manuals aren't (the game even had a clay pigeon mode which was clearly there to prove it's only fun to shoot things that have faces). Also, a lot of us weren't old enough to read in 1985.
Our failure to do so, however, robbed us of the joy of killing things that had faces and the cursing voices of our friends. All you had to do was make sure you had a firm grip on the Zapper and plug a controller into Port 2 in "Single Duck" mode.
The control pad is now controlling the duck. Now go get your NES out of the garage and try it.
Check out more from Luke with The 5 Most Retarded Causes People Are Actually Fighting For and 5 Books That Can Actually Make You Stupider.