A Christmas Carol (2019): The opening scene where Marley's grave is peed on. That alone should let you know just how dark this adaptation is. And that's not getting into Scrooge's sister wielding a gun against Scrooge's headmaster.
Crisis on Infinite Earths (2019) has the death of Oliver Queen, founding hero of the Arrowverse. Then he kinda-sorta comes back as the Spectre. And then he sacrifices himself again. Unlike so many others who fell prey to Death Is Cheap, he is absolutely, truly, and definitively Killed Off for Real.
"The Name of the Doctor": John Hurt unexpectedly appears in a place he shouldn't be, and then turns to face the camera as an on-screen credit informs us who he's playing: a previously unknown incarnation of the Doctor.
"Spyfall": The first part became legendary within a day of its premiere for its jaw-dropping cliffhanger featuring the utterly unexpected return of the Master. The second part followed suit by revealing the Master had destroyed Gallifrey due to an Awful Truth involving the "Timeless Child".
"Fugitive of the Judoon": Fan-favourite character Captain Jack Harkness unexpectedly returned over a decade after his last appearance on the show. And this was only the second-biggest surprise of the episode, as the reveal of the titular fugitive as another Doctor sets the era's Myth Arc into motion.
"The Power of the Doctor": It had been previously announced that Ncuti Gatwa would be taking over from Jodie Whittaker, so to see her "unregenerate" into David Tennant once again is quite a major shock. However, people had theorized this beforehand, since the specials in 2023 were reported on prior to this episode airing, and filming shots showed Tennant and not Gatwa, but it wasn't yet known whether Whittaker would de-regenerate into Tennant, if the specials would be flashbacks of previously-unknown adventures, or if it would involve the "clone" of the Tenth Doctor created from his spare hand. The fact Tennant wore a different outfit helped add fuel to the fire.
"The Giggle": The Fourteenth Doctor's regeneration. Everyone knew it was coming, but nobody could have possibly predicted that it would be a bi-generation, with Fourteen and Fifteen existing together.
Game of Thrones is infamous for doing this sort of thing (as is its source material, A Song of Ice and Fire). The most infamous example is probably the Red Wedding, in which Robb Stark, his pregnant wife Talisa, and his mother Catelyn were betrayed and murdered in cold blood, although killing off its Decoy Protagonist got the show quite a bit of attention too.
The Good Place has the reveal that the paradise our protagonists are living in is actually The Bad Place, completely flipping the show on its head in the process.
For House of the Dragon, Lucerys' death is easily the most shocking and terrifying moment of season 1. From shot of Vhagar flying above him to highlight how huge she is, to chasing him through the canyon and when he expects less, she launches an attack devouring both Arrax and Lucerys.
In the Direct to Video movie Kamen Rider W Returns: Kamen Rider Eternal, the main villain is a scientist who kidnapped multiple people and imprisoned them inside his special prison camp, called 'The Village', in order to create telekinetic super soldiers. Katsumi, the main character, spends the entire movie trying to free those prisoners, only for them to die after leaving the prison camp, due to having implants in their heads. After the villain starts to gloat about this, you just know it's time for ass kicking.
NUMB3RS: In the third season finale it is revealed that Colby Granger has seemingly been working with the Chinese, a fact that devastates the team, especially David. It isn't revealed until the fourth season premiere that he is actually undercover to find the mole and nearly dies before he is saved.
The scene of Zeff and his leg shocked many viewers who were used to the anime, where Zeff cut it off to save Sanji from drowning instead. And those same viewers who thought that the Autocannibalism was an especially dark adaptational change tend to be even more surprised that this was how Zeff originally lost it in the manga.
Also the scene where Zoro cut Mr. 7 completely in half. Many first time viewers of One Piece, and even the long-time fans, were surprised at the extent of the gore and violence displayed, having thought that this was just a light-hearted romp of adventure.
Helmeppo's full display of his backside had viewers momentarily stunned.
Orphan Black gets into the action with the episode "The Scandal of Altruism", a major case of The Bad Guy Wins and Downer Ending. Kendall Malone, from whom both the Leda and Castor clones were cloned (due to Bizarre Human Biology), is shot and immolated, apparently destroying all traces of her genetic material. This leaves the clones, several of whom possess severe genetic illnesses, with a major recourse to unlocking the cause of these illnesses now closed to them. Additionally, Cosima's research on her illness and genetic code is seemingly destroyed, rendering her last several months' worth of work futile. As icing on the cake, we are told that Delphine is dead and learn that Beth Childs was blackmailed into committing suicide, as she was threatened that if she did not do so, the other clones would be killed. Of course, the faction responsible for this turns out to be the same faction responsible for Kendall's murder and the destruction of Cosima's research. The show has had Wham Episodes before, but nothing approaching how devastating this episode was. It's almost a Game of Thrones-level gut punch.
Psych: Henry getting shot by a corrupt colleague in the Season 6 finale. We don't even find out if he survives till the Season 7 premier, which aired 10 months later
One episode starts with Maria, Luis, Gabi, and Big Bird innocently playing charades but then Maria suddenly cries out in pain! It turns out she has a stomach virus.
One episode begins with Gabi and Luis goofing around together, but Luis suddenly cries out in pain and grabs his back. It turns out he's thrown his back out.
In "Crossfire", Odo's been jealous because he has a crush on Kira, who has a boyfriend. Then, he throws things in his quarters around without warning, despite usually being an exaggerated Neat Freak.
In "Hard Time", O'Brien is having trouble after thinking he's been in prison for twenty years when it's really only been a few days. Then, there's a scene where he tries to commit suicide.
"I Shot an Arrow Into the Air": A spacecraft lands on what the astronauts believe to be an unknown asteroid. One astronaut is so obsessed with survival that he kills his fellow astronauts for water. Then it's revealed that they never left Earth, and he has killed his partners for nothing.
"Time Enough at Last": A nuclear fallout has left Henry Bemis the last man alive, but he at least can entertain himself with books. But then his glasses break.
"The Eye of the Beholder": The Reveal that Janet Tyler's face, which she has been angsting over the whole episode, is actually pretty, and everyone else is ugly (to our standards).
