Mobile Commandos go over the three greatest old-school unlockables to help you get your retro on: "Easter eggs about as old as gaming itself, adding intrigue and establishing a playful line of communication between player and designer. The most fun secrets lead to unlocked game elements, rewarding you for your hard work playing (or looking up codes) with new tools and functions, but the best of those are the unlocked characters. The examples below show three famous badass unlocked characters, each accessible in totally different ways, each interacting with the player in different ways as well."