Files hidden in the extremely large Mass Effect 3: Extended Cut DLC update have shed a light on some future story-based DLC for the game.
WARNING: THE FOLLOWING CONTAINS SPOILERS ABOUT THE STORY OF AN UNRELEASED PIECE OF MASS EFFECT 3 DLC.
In the mission, Shepard attempts to rescue a scientist named Ann Brynson, who's trapped in a mining facility, which fell into Leviathan's control ten years before.
In pieces of dialogue, Leviathan is called a "defector" and a traitor for killing one of his own kind. One particularly interesting line refers to Reapers' creators.
"So the Reapers did not fully exterminate their creators. That suggests they are fallible, even on large or long-term scales."
At the end of the DLC, Leviathan can join the battle against the Reapers, presumably as a War Asset. Dr. Brynson can either live or die, depending on Shepard's choices.
The DLC won't actually be Leviathan's first appearance in the Mass Effect universe. In the original ME, scanning a planet revealed the "Leviathan of Dis", the "corpse" of a living starship. In Mass Effect 3, Balak - a character from the Mass Effect DLC "Bring Down the Sky" - may or may not indicate to Shepard that Leviathan was a dormant Reaper, which the Batarians reactivated by mistake.
Separately, Mass Effect 3 producer Mike Gamble teased fans with word that information on new DLC was coming soon on Twitter: "As I've said before, we do this for you! EC was our gift to the fans. Hope you enjoyed. Also... keep your ears open over the next little while."
Bioware will be hosting a panel at Comic-Con in San Diego next month. That sounds like a good time to roll out some Mass Effect 3 DLC plans...