With the advent of downloadable content, developers are able to add to and change numerous elements of games that have already been released. Most of the time, this content comes in the form of extra gameplay that can be played during the campaign, new post-game content, or additions to a game's multiplayer suite. However, on rare occasions, developers have also used downloadable content and patches as a means to change the actual ending of a released game's story. Some examples of such are listed below.
The game Fallout 3 originally ended with the player's unavoidable death. However, Bethesda changed this ending with the release of the first DLC expansion, Broken Steel. With this change, the player is now able to survive the endgame by sending an allied character to perform the final task required. After being knocked unconscious, the player awakens, able to continue exploring the world after the final story quest is completed. The actual content of the Broken Steel expansion is also accessible beyond this point.
The game Portal originally ended with the protagonist Chell managing to escape the Aperture Science facility. However, a patch to the ending added an extra scene where she is captured in the parking lot and dragged back inside, setting up the events of Portal 2.
Mass Effect 3
Upon its initial release, Mass Effect 3 received heavy criticism for its endings, which many felt were too similar in their content, were almost entirely unaffected by the choices the player made over the course of the trilogy, and contained numerous plot holes. In June of 2012, Bioware released a free downloadable update to the game called "Mass Effect 3: Extended Cut," which added more cinematic content to the game and altered some existing scenes in order to both provide more clarity and closure.