Cinematic sequences to expand upon the ending.
Mass Effect 3: Extended Cut was released at approx. 2:30 PST on June 26th. It was created to all clarity and closure to the Mass Effect 3 ending, which has sparked a lot of debate and controversy. The free DLC adds new cinematics to enhance the ending and give players a better sense of what happens in the ending.
Extended Cut adds a new option as well: Reject. You can reject all of the Catalyst's options and are given a new ending.
Extended Cut: Destroy Ending