Mass Effect 3: Extended Cut Reveals Leviathan DLC

There's been another Mass Effect 3 script leak, only this time it involves a new "Leviathan" DLC that was uncovered from the Extended Cut content by a sleuthing member of BioWare's forums and then posted to Pastebin. Since Eurogamer already read through it, I'll share their summary, though caution is suggested since spoilers abound:
Shepard is sent to rescue the scientist Ann Brynson, who you find at a Reaper-indoctrinated mining facility. The colony has been controlled by a Reaper named Leviathan for 10 years.

Leviathan is referred to as a defector, a traitor who killed one of its own kind.

One dialogue line hints to more information about the Reapers' creators, briefly alluded to by the Star Child in the game's ending.

"So the Reapers did not fully exterminate their creators. That suggests they are fallible, even on large or long-term scales."

Leviathan can then join the fight against the other Reapers, presumably becoming a War Asset. Brynson can either live or die based upon your choices.

A Reaper named Leviathan has been mentioned before in Mass Effect lore. Scanning a planet in Mass Effect 1 revealed "The Leviathan of Dis", the corpse of a presumed-dead living starship. Then, in Mass Effect 3, the character Balak (if kept alive in Mass Effect 1 DLC Bring Down the Sky) hints that the Leviathan was a dormant Reaper, which the batarians have accidentally reactivated.