9 Full Video Games You Can Unlock Inside Other Games
4. Donkey Kong (Inside Donkey Kong 64)
It's easy to forget - simply because it was ludicrously hard - that Donkey Kong 64 mandated you play through 8 levels of the original Donkey Kong to actually finish the game.
Making it so you need both the Rareware Coin (obtained from beating 1983's Jetpac in-game too), plus the Nintendo Coin to access the final area, the fact Rare included a Donkey Kong cabinet in DK64 feels like a secret, because everything about this process was so hard to figure out.
Found inside the Frantic Factory level - but only after you've got the Gorilla Grab from Cranky to pull an activating lever - this actually beat-able version of Donkey Kong will give you the necessary coin after surviving two sets of four levels.
You have to do each set on one life as any mistakes will take you back to the beginning. In short it was a living hell, and the sole reason more people didn't finish Donkey Kong 64.