Lost does this a lot. It tends to cross over with Mind Screw. Notable examples:
- "Walkabout": John Locke was paralyzed before crashing on the Island, but can mysteriously walk again.
- "Raised by Another": It's revealed that Ethan wasn't on the plane. Then he captures Claire and Charlie.
- "Deus Ex Machina": Locke and Boone find a suspended plane and finally make contact, only to mishear that there weren't any survivors on the flight. The plane falls with Boone in it, leaving Locke to bring Boone to Jack in an attempt to save his life, only to run back to the Hatch and see a light shine out of its window. In the next episode, Boone dies right when Claire gives birth.
- "Exodus, Part Two": The Others confirm that they are in fact real by shooting Sawyer, blowing up the boat with Michael and Jin on it, and kidnapping Walt. The hatch is finally opened, and it's a long way down.
- "Man of Science, Man of Faith": Someone's living in the hatch! And Jack's met him before!
- "Two for the Road": Michael murders Ana Lucia and Libby, then sets "Henry" free.
- "Live Together, Die Alone": Turns out that guy living in the hatch crashed the plane, almost causing The Incident to happen. And the hatch blows up with Locke, Eko, and Desmond trapped in it. And Jack, Kate, and Sawyer are captured so that Michael can go home with Walt. And someone in the outside world, that being none other than Penny from this episode's flashbacks, learns where the island is.
- "The Man from Tallahassee": Locke's dad is on the island.
- "Catch-22" and "D.O.C.": Someone arrives on the island. And she says that the wreck of Flight 815 was found, with no survivors.
- "The Brig": Where do you even begin with this one? Locke returns after being missing for the last few episodes. He forces Sawyer to kill his father, which he ends up doing after Sawyer learns about the role Locke's father has had in his life. Locke tells Sawyer about the Others' plan and runs off. Also, after trying to keep the pilot a secret from Jack, Kate goes and tells him anyway.
- "Through the Looking Glass": The flashback is actually a flashforward! Some people get off the island, but they aren't happy about it. Also, a lot of people (mostly Others) get killed.
- Season four finale: in "There's No Place Like Home, Part II": Ben moves the island, Michael and many of the Flight 815 survivors are blown to pieces, Locke becomes the leader of the Others, and Desmond reunites with Penny before they send the "Oceanic Six" on their way....and in the flash-forward, Locke is dead.
- And the Season Five finale "The Incident: Parts One/Two" tops them all: we finally meet Jacob, and it turns out he's interacted with all the main characters at important moments in their lives. It turns out that the guy we've believed to be Jacob all this time is actually his nemesis, which carries some pretty staggering implications, especially about Jack's dad. It turns out Locke is still dead, and the man walking around alive is actually Jacob's nemesis, who manipulates Ben into killing Jacob. And in the past, the eponymous Incident occurs, so at first it seems Jack's plan to change the past has failed. Then Juliet is dragged into the Swan pit, turns out to be not quite dead, and sets off the nuke herself. Just to make it clear how totally wham this is the ending title card is flipped to black text on a white background. Nothing Is the Same Anymore. Boom.
- "Sundown". Sayid kills Dogen, allowing the Monster to invade the Temple and completely eradicates all the Others who didn't join him. At the end of the episode, everyone who might oppose Smokey is dead, scattered, or fleeing for their lives, and Kate can only look on helplessly as Claire, Sayid, and the surviving Others join Fake Locke.
- "The Candidate". The survivors reach the plane, and decide to hijack the submarine instead due to the plane being rigged with explosives. They board and betray Un-Locke at the last minute, leaving him stranded. As soon as they think they're safe, they find the armed bomb that Un-Locke snuck into one of their backpacks. It blows up, resulting in the deaths of Sayid, Jin and Sun, while Jack, Kate, Hurley, and Sawyer escape, mourning their lost friends. Un-Locke takes notice, and heads off to "finish what he started".
