All of these are AU, of course.
Battlestar Galactica/Kings: The barely living remnants of the fleet -- for instance, Kara, Lee, Baltar, the Final Five and the "good" skinjobs -- land in Gilboa. Everything goes great at first, until the allied Cylons and representatives of King Silas' regime come to blows over who God's "chosen" people really are. War begins...
The Prisoner/Lost: Would have been amazing if McGoohan were alive still. In any event, in season 3, instead of taking Locke to the cabin, Ben takes him to an area covered in foliage and muck, clearly hidden by years of poor care...or years of wanting to be hidden. Ben confesses to Locke he made up the name Jacob to hide the identity of the great man he truly serves. No one, not even Tom or Richard, will ever truly know who leads The Others. Ben, finding an intercom on the structure, presses it. We begin to see the shape of the building and recognize it as a sort of green dome.
Ben: Sir, it's Linus. We're here to see you.
A crackly, older voice on the other end: We?
Ben: Yes, sir, I have John Locke with me.
There is a buzz. The doors open. Led by a small butler, Ben and Locke find their way through a hallway into a main room, a circular, robotic chair facing away from them. It begins to slowly turn.
Locke: Ben, what's going on? Where am I?
The chair has fully turned now. Seated in it is now an old, broken Number Six, wearing a Village pin with an unidentifiable number on it.
Six: In the Village.
Locke: What? Ben, who is this? What is this place?
Six: Linus, take your leave of us for now. The Butler will serve you tea in the foyer.
Ben, concerned: Thank you, sir.
Ben and The Butler exit.
Locke: What's going on here? What do you want with me?
Locke: In...information? About who? The Others? The Survivors? Something else? Whose side? Who are you really? Whose side are you on?
Six: That would be telling. We want information. Information. Information.
Locke: I can't trust you. I don't even know you. I won't let anyone get hurt. Not here, not now, not ever again. The Island speaks to me! I have to do what's best for it. This information you want? You won't get it!
Six: We will. By hook or by crook, we will.
Locke: Who...what's going on here? Who are you in all of this? What's Ben got to do with this? What's his part?
Six: The New Number Two.
Locke: Number Two? What--who...who's Number One?
Six: You are Number Six.
Locke: I'm not a number. I'm a person. Don't tell me what I am. Ever.
Six: Haha. Hahaha. Hahahahahaha.
Maniacal laughter continues and is drowned out by BOOM - Lost, and then a slight hint of the old Prisoner theme...
Yeah, THERE'S your game-changing twist. Eat it, flashforwards.
You heard me.