The term unlockable games refers to full video games that can be unlocked within another video game, often as easter eggs. Often these unlockable games are earlier entries in the series of the game in which they are hidden, and they become available after beating the game or meeting other requirements.
The PC game ' by LucasArts included its predecessor Maniac Mansion.
In the Sega Saturn release of Duke Nukem 3D, Death Tank Zwei can be unlocked either by shooting every toilet in the game or by having a save file from another game by Lobotomy Software.
In Donkey Kong 64, the games Jetpac and Donkey Kong can be unlocked.
In several Grand Theft Auto games, various arcade games can be unlocked by finding their arcade machines.
Metroid was an unlockable in two different games: it could be unlocked by finishing Metroid Fusion and connecting it to Metroid Prime with the Nintendo GameCube Game Boy Advance Cable, and in ' it becomes available after beating the game.
In ', it is possible to unlock Mortal Kombat 2 by either completing the story mode with Smoke or by entering a cheat code at the menu.
The Xbox version of Ninja Gaiden contains the first three Ninja Gaiden games for the Nintendo Entertainment System ported from the Ninja Gaiden Trilogy compilation for the Super NES, while the Black re-release on the same system features the Ninja Gaiden arcade game instead.
In Pac-Man World 2, players can unlock the following four Pac-Man games by collecting tokens: Pac-Man, Ms. Pac-Man, Pac-Attack, and Pac-Mania.
In ', you can unlock the Pitfall!.
In Project Gotham Racing 2, Geometry Wars is unlocked by entering the garage, entering walk mode, walking to an arcade machine, and pressing A.
In ', players can unlock Prince of Persia. In the Xbox release, Prince of Persia 2 is also unlockable.
In Return to Castle Wolfenstein, Wolfenstein 3D is unlocked after the player completes the game.
Shenmue on the Dreamcast contained the arcade games Hang-On and Space Harrier, which could be unlocked by walking into the arcade and using in-game money to play.
In Sonic Mega Collection, players can unlock five games by playing a certain number of times: Blue Sphere, Sonic & Knuckles, Sonic & Knuckles , Ristar, and Flicky.
In ', Star Wars, ' and ' can be unlocked.
Super Smash Bros. Brawl has a feature that allows the player to play demos of the characters' games of origin, but the demos have a strict time limit, after which you are returned to the menu.
' features the 1989 Teenage Mutant Ninja Turtles arcade game, while ' features '.
Tekken 5 includes the first three Tekken games and StarBlade.
In ', versions of Centipede and Missile Command can be unlocked by finding their arcade machines in the game's levels.
In ', Zork I can be unlocked by typing "Zork" into an old computer at the menu.
In Splatterhouse , the player can unlock the original Splatterhouse and its Genesis sequels.
In Super Mario Bros. Deluxe, the player can unlock Worlds 1 through 8 from the by beating Luigi's high score 300.000 in the original mode.
In Sonic Generations, the first Sonic game, Sonic the Hedgehog can be unlocked.
