Unlockable content refers to content that is available in video games but not accessible unless something is performed by the player to get access to it. Different genres of games have different styles and options of unlockable content that is standard among their games. The unlockable content varies, and can be as little as a single weapon or enhancement, to more than doubling the playable characters available to the player.
Methods
Presale exclusives
Many games, such as Left 4 Dead 2 and , offer presales that come with exclusive unlockable content. In order to get these exclusives, one must order the game through the retailer before it is available for sale, with a small deposit to guarantee the game. Once this presale is made, the buyer gets a code to use to get the unlockable content once the game is available. This has been done by many companies world-wide, such as North America's Gamestop, UK's Game and many other retailers.
Achievements
Some games have established replayability for players through a rewards system. Once the player does unique or difficult actions in a game, such as killing a boss in a limited time, or collecting a certain number of items over the course of playing the game, the player can earn a reward, potentially unlocking more content, such as additional items for the player to use or vanity items to show the player's prowess at achievements. This extended into a form of metagame with the release of the Xbox 360. The system included a "Achievement System" by which certain in-game achievements would be recognised and rewarded with an "achievement" - a small image and description of the achievement, along with a score value, which is added to the user's total Achievement Score and displayed on their profile. This was followed up by the PlayStation 3 and Steam PC videogame distribution system who patched in PlayStation Trophies and Steam Achievements systems, respectively, and the continuance of these systems in the Xbox One, PlayStation 4 and PlayStation Vita. The metagame focuses on "completing" a game by collecting all of its Achievements/Trophies. While Steam's metagame is limited by its lack of overarching counter, part of the metagame on PlayStation and Xbox is increasing your overall score by collecting Achievements/Trophies in multiple games. These Achievements/Trophies can be given for story/level progression, difficulty level, completing a number of actions, completing a difficult action, and more. These Achievements/Trophies need not be connected to any in-game reward. Companies such as Ubisoft have released programs and systems that take advantage of this metagame, by rewarding players who complete certain actions with points. These points, known in Ubisoft's Uplay service as "U" points, can be redeemed for in-game rewards such as additional in-game currency, character skins, missions, weapons, and the like.
Defeating bosses
Especially with fighting games, defeating certain bosses or villains can unlock those characters, or other non-starting characters, as playable characters for the player. Games like Tekken and Soulcalibur offer such methods of unlocking content.
Internet usage
Sometimes, the only action necessary to unlock new content is internet availability. Games like Professor Layton and the Curious Village offered players additional puzzles every week by downloading the puzzles from the internet over the Nintendo WiFi Connection available in all the Nintendo DS handhelds.
Hidden items
Sometimes a player can unlock content by collecting hidden items found throughout the game. Some games offer a purchase system of additional content, such as images, wallpapers, music and such, great example is the .hackvideo game series, by collecting the hidden items and redeeming them for the unlockable content. Sometimes the player can get these unlockables based on the total amount of hidden items found.
