Spoilers ahead. So much for the extended cut of Mass Effect 3 just adding a slideshow to the end of the game's many possible endings. It appears that development studio BioWare has given players a new option at the game's final junction.
Instead of choosing to synthesise with the Reapers, destroy the Reapers (and Geth) or take command of the Reaper, commander Shepard can tell the star child to go to hell and refuse to make a decision. (A user on the BioWare forums claims you can also just shoot the kid to literally trigger this new ending. We've not done this ourselves.)
Note: we have not encountered this option ourselves but believe the widespread conversation of it online among fans and a clip of it on YouTube prove this is not a hoax but in fact a real new option. We're racing to the ending ourselves and will confirm when we've gotten there.
Here's the new refusal ending.
The new choice appears to be available from a new batch of dialogue options seen in this shot atop this story, which was snapped overnight by NeoGAF message board user CrewNH.
The original version of Mass Effect 3 presents only the options seen in this shot and then allows Commander Shepard to choose among three possible final acts.
Mass Effect 3 EC | New Refusal Ending [YouTube]