Legato's introduction in Trigun pulls this off in a single frame. It's a bright and sunny day, the kids are playing with Vash. Then out of nowhere, Legato. He killed and ate the friendly shopkeeper Vash was just speaking to, and feels it would be a downright shame if the little girl Vash just bought an ice cream for would have to be next. The entire scene is completely horrific, but what cements it as this is the opening shot of the usually lighthearted and goofy Vash looking legitimately terrified for the first time in the series that clearly indicates exactly how bad things are about to get.
Legato: ''If I'd felt like it, all the people within a 50 meter range, in 0.2 seconds, would all be dead... In the next ten minutes, you'll learn the true meaning of hell."
It's also implied (and stated in the manga) that the hot dog he gave the little girl was made from the remains of the aforementioned shopkeeper. Yikes.
Gantz was already a pretty dark series, but it still manages to give us this somewhere around the end of volume 9 with the death of THE ENTIRE TEAM except for Kurono. The fact that Kuronotakes a level in badass afterwards does nothing to mitigate the new knowledge that Plot Armor has ceased to exist.
Digimon Tamers has loads of them, but the two most prominent happen to the same characters, but in different ways, in episode 34 Jeri's partner, Leomon, is killed then absorbed by Beelzemon, and there's no Village of the Beginnings in this series., Later on, after Beelzemon's Heel-Face Turn, Jeri has been trapped by the enemy, and just when things seem to be hopeless, Beelzemon uses all his strength in to a single attack, Fist of the Beast King, which is Leomon's signature attack, and is then able to let Jeri free... if only she hadn't been too shocked by remembering her partner through his killer, and not being able to actually leave her imprisonment, and uttering the line You're... not... Leomon, distracting Beelzemon long enough for him to be brutally stabbed in the back, you know, for kids!.
Kamina's brutal death in Tengen Toppa Gurren Lagann was not only a legendary Tear Jerker, but the event that changed the series from a fun, colorful, lighthearted adventure romp to an epic war story on a massive scale. The fan reaction to this event is polarizing to this day, and the show aired more than half a decade ago.
Mazinger Z: The last third of the anime series was getting increasingly darker due to the new enemies: Professor Morimori was murdered, Aphrodite A was definitely destroyed -which, believe it or not, was a great deal and Sayaka got an Heroic BSOD cause it-, Kouji and Shiro's mother returned only to be revealed she was an imposter -poor Shiro was forced to shoot her in spite of he was not sure of she was not his real mother-... and then you have the final episode: the heroes have triumphed over Dr. Hell and return to his Home Base... only to find out one of the Co-Dragons was secretely working for a Bigger Bad. Two unknown Robeasts appear, easily destroy the Institute, Diana-A and Boss Borot, and when Kouji goes to fight them, they easily and mercilessly trash the erstwhile apparently invincible Mazinger-Z.
This episode was better developed in theMazinger-Z vs Great General of Darkness feature. Several Mykene War Beasts laid waste to New York, Moscow, London and Paris in one single day before heading towards Tokyo. Kouji sortied to fight them and was completely trounced as they burnt Tokyo to ashes. Meanwhile back in the Institute another War Beast strikes, bringing down the place. Shiro gets badly wounded when a ceiling crumbles down on him, and falls into a coma. At the next morning, another squad of War Beasts attacks, and Kouji deploys Mazinger-Z in spite of he is badly injured and weakened and his robot is unrepaired and power-depleted. He gets outnumbered and is being easily defeated. However, Boss manages to destroy one of the Beasts out of sheer luck, and the cast breathes relieved for a second... before the Beasts easily get rid of Boss and return to trash around a helpless, powerless Kouji.
Great Mazinger: In the Gosaku Ota manga the punches started when the Mykene blew up a coast city after Great Marshall of Darkness replaced the former deceasedDragon-in-Chief. In a few episodes the Japanese army threw an attack against the heroes and their Home Base, Prof. Kabuto went through a Despair Event Horizon, the Fortress of the Science got destroyed, forcing the heroes to run away and lie low, the Mykene burnt Tokyo to ashes, conquered Japan and crafted a Kill Sat, obliterating whole cities. Then you have the Final Battle. The heroes were busy building a new Home Base when the Mykene army launch an attack. Misato gets sliced in half in front of Tetsuya as he is unable to do anything, Mazinger-Z and Great Mazinger are trashed, Prof. Kabuto dies to save Tetsuya, and in reaction Tetsuya, realizing it was his blame commits a Taking You with MeHeroic Sacrifice. The Final Battle in the anime version was not quite so brutal, but in exchange you had a scene where Prof. Kabuto dies in arms of his son Kouji.
UFO Robo Grendizer: In the Ota chapters both sides loses the war. The Vegan invaders are destroyed, but Duke, Maria and Sayaka die and The End of the World as We Know It happens. Only Kouji and Hikaru are left alive. It was lucky Grendizer was the last series in the original saga, because you get to wonder how the creators could have gone one.
Shin Mazinger Zero: This series is Mazinger Z orginal manga -that was pretty darker than the series and posterior Super Robot shows- Meets Neon Genesis Evangelion. So, what you have when you blend an Unbuilt Trope with a Deconstruction? In the first arc, Kouji and Sayaka go to meet Kouji's grandfather. Hey, that is Kouji's father! Scratch that, it is Kouji's father head! Dr. Kabuto has turned mad(der) and has beheaded his own son? And now he is trying to offing his grandson? He has just raped and murdered Sayaka impaling her with a dozen of metal rods? And Kouji has killed him in turn, losing one arm? And now Mazinger has absorbed Kouji? Wait, that is not a "normal" Humongous Mecha, that is a Eldritch Abomination... that has just destroyed the world. Then again, it had been completely overrun by Dr. Hell's armies, so there were little left to save. Let's reiterate this is the first arc.
The fight with the 13th angel. It's generally agreed by fans that this is the point in the series when things started to take a turn for the worse.
The fight with Arael. Hey, it looks like the cast is starting to resolve its issues and the show might be heading towards general mental stability! You know what would be really fun? How about breaking out the Trope Namer for Mind Rape?
Bleach: The beginning of the final arc is a huge change in how Bleach generally works, powered by a series of these in quick succession:
You know how fans joked that Tite would never kill off any main character or hero? Yeah, um, Chojiro Sasakibe, second-in-command for Yamamoto? Dead. Bloodily.
The general rule was that two of the villains would confront and defeat Ichigo in a fight, to establish one as The Rival for that particular arc. It happened with Renji Abarai and Byakuya Kuchiki in the Soul Society arc and Grimmjow Jaegerjaquez and Ulquiorra Cifer for the Arrancar arc. Enter Asguiaro Ebern, who attacked Ichigo on Earth and escaped after failing to steal his Bankai. In Soul Society, Luders Friegen declared war on Soul Society by murdering Chojiro. He was The Rival to Ebern, which fit the general dynamic of the former villain pairs. It seemed like Luders and Ebern were set up to be major antagonists for the duration of the Story Arc. Before they could do anything else, their boss murdered both of them for incredibly minor infringements. Turns out their role was actually to warn the reader about just how vicious the new villain was.
The Vandenreich are shockingly effective compared to previous villains—and to antagonists in most Shōnen. Talking Is a Free Action? The Vandenreich will attack you while you're lecturing them. We didn't even learn most of their names until after the initial fighting was over. Awesomeness by Analysis? They avoid bragging about their secret techniques and attack the science division early on to prevent said techniques being reverse engineered en masse. Honor Before Reason? The Vandenreich give the Soul Society five days to prepare for the war and invade later that same day. Heroes bust out their greatest ability only once they're fully enraged? That just leaves an opening for a Megaton Punch. Hell, the entire basis of the Vandenreich's strategy is to strip captains of said greatest ability, leaving Soul Society's best and brightest largely defenseless. Villains prefer to let the smoke clear before attacking? Bazz-B uses it as cover for an ambush. The Sorting Algorithm of Evil? Consciously inverted: they send their elites in first to hammer the heroes before sending the foot soldiers to Zerg Rush the survivors. Named characters always prevail? Within minutes of the invasion, the 6,000 strong Gotei 13 has just under 2,500 casualties. Established characters like Kira, Byakuya, Renji, Rukia, and Kenpachi are utterly trashed, some of which occurred off-screen.
Yamamoto, the strongest Shinigami in the series, finally uses his long-anticipated (and appropriately frightening) Bankai, easily defeating his opponent... only for said opponent to reveal that he wasted his greatest ability on a decoy. The real Yhwach shows up, steals Zanka no Tachi and proceeds to slice Yamamoto in half, taking the time to cut off his arm, stomp his head to the ground and obliterate his corpse just to make sure he's gone.
You know the whole tirade of the Next Tier Power-Up, right? How the hero gradually gains more abilities as the plot progresses? That was Ichigo Kurosaki's MO. Renji was often saddled with The Worf Effect. When the two are given a chance at real training, Ichigo fails to pass, and it's Renji who succeeds. For an extra shiv, Ichigo gets kicked out of the Soul Society and sent back to his home, because he's not actually using a real Zanpakuto. The experience forces Ichigo to reconcile with his Inner Hollow in order to continue the training.
Everyone had waited years for the flashback arc that would finally reveal how Isshin and Masaki met and got together, which sounded like pure ditzy fun (given the personalities involved). Especially once Aizen claimed he'd been keeping an eye on Ichigo since before he was born, which added intrigue and Evil Is Hammy opportunities to the idea. When the Everything but the Rain arc arrived, many questions were certainly answered, but what no-one in the fandom had expected was just how thoroughly Ryuuken's life would be ruined in the process. A fun and ditzy arc? Not even close. Grey Rain Of Depression? Yeah, Ichigo doesn't have the monopoly on that anymore. By the arc's end, even fans who used to be ambivalent to Ryuuken wanted to give him a hug.
There are a lot of characters who inspire BrokenBases in Bleach, even CHAD sometimes, but there is one who's universally adored. One whose marble pedestal Kubo himself just shattered into tiny bits? Zangetsu. He's revealed to be NOT the manifestation of Ichigo's Shinigami powers, but his QUINCY powers (from his mother's side of the family)... and he resembles the same man who caused his mother's death. He hasn't actually been helping Ichigo; he's been holding Ichigo back all these years, because he'd have to kill him if he ever became a true Shinigami. Zangetsu isn't even his real name, it belongs to Ichigo's inner Hollow, his true zanpakutou. And in order to reforge his bankai, Ichigo has to say goodbye to "Zangetsu" forever.
One Piece had the deaths of Portgas D. "Fire Fist" Ace and Edward "Whitebeard" Newgate in the climax of the Paramount War. Up until then, One Piece got saddled with the term "Nobody dies in One Piece".note Albeit with the "out of flashbacks" qualifier, since people often die in characters' backstories It has the added bonus of a literal gut punch, in the case of the former.
Mai Hime has the loss of Akane's child, and the resulting death of her boyfriend Kazuya, showcasing what is at stake for the Himes.
In the Wham Episode of Mai Otome, the turning point in Arika and Nina's characterization is the death of their mutual friend Erstin at Nina's hands, not long after she had been revealed as The Mole.
City Hunter features them periodically to remember the reader that it may be a comedic series but the protagonist is still a wanted criminal that the police leaves alone only because he always goes after much worse criminals and tries to limit the body count.
Psycho Pass was dark from the start, being a show about a Dystopia controlled by The Sibyl System, which has made feeling any extreme emotion, mental illness or thinking differently from the masses illegal. The antagonists that the Ministry of Welfare and Public Safety Bureau took down already included all kinds of criminals from a suicidal rapist to a Mad Artist who likes turning her victims' corpses into art. The show doesn't seem like it could get any darker, and then after Shinya defeats SengujiToyohisa and saves Yuki, one of Akane's best friends, Shinya falls unconscious due to being shot. Sadly, Makishima appears at that moment and kidnaps Yuki and lures Akane with her. Makishima gives Akane the chance to save Yuki, if Akane can shoot him with a shotgun. Akane tries to use the Dominator on him, a weapon which can only kill someone if the Sibyl System judges them as as mentally unstable or not pure of intention. It doesn't fire, as Makishima genuinely believes in his actions being normal and justified. Makishima gives Akane one more chance to shoot him, and Akane can't do it. Makishima then slits Yuki's throat, and after the next episode being a prequel episode, Makishima then proves to be more dangerous than all the other antagonists who only hurt or ended a few lives...Makishima aims to break down all society, and actually succeeds for at least a few weeks. Even after being caught, he escapes and continues upping the ante.
The season 1 finale of Sailor Moon. When Sailor Jupiter is killed, it's the start of the punch. Then when Sailor Mercury follows her, you just know the rest of the characters aren't safe.
Two in Attack on Titan. The revelation that Annie was the female Titan who brutally killed all those members of the Survey Corps and Levi's own personal squad right after Eren started to trust them; and if this wasn't enough, right after that Reiner and Bertolt are revealed to be the Armored Titan and the Colossal Titan respectively.
Before Watchmen: Minutemen explored the titular Minutemen in their Golden Years, showing their successes, their infighting, and some darker themes, like The Silhouette's investigations into child murder and pedophilia. Then in issue 4, she and her partner are murdered in their beds after she's kicked off the team. After this, the real mental toll and questionable morality set in, as characters die or leave, and the Minutemen fade away.
In the second Grave Academy book's finale, Jack and Sophie are able to save Robin from Teresa's Mind Control, but her soul'd being under the influence for so long that she begs Jack to Mercy Kill her, he does..
A bit earlier in the same chapter, Jack and Sophie discover that Jack's sister, Teresa, who appeared to be just a victim, was pulling the strings all along, the she goes psycho on them and slices her brother's eye off, and almost kill them and their students, only for Jack to deem her beyond saving and ends up killing her in self-defense.
That's NOTHING compared to the last book, which started Lighter and Softer, only to shock even more with Samantha's sacrifice, killing off one of the most beloved and sweet characters in the story, and it ended up being useless, as instead of preventing the onther's deaths, most of them actually die before the final battle, and then, ALL of them, save for Luke, die at some point during the final confrontation..
Chapter 4: Hitomi, having gotten her first taste of using Mind Control to make her victims kill other people and themselves, uses her powers to cause a massacre at a diner, resulting in the deaths of 20 innocent people, and showcasing that the SUEs mutual (if varying) lack of regard for human life.
Chapter 18 and 19: While previous SUE attacks had interfered with the canon villains' plans, Bachiko and Meiko's plan provides Ishigami and Nagi the opportunities they need to put their plans into motion; the former results in his and Yukariko's deaths, while the latter results in Shiho and Mai being forced to fight like in canon, with Yukino barely managing to defuse the situation by arriving before Mikoto and knocking out Shiho.
Chapter 21: the Obsidian Lord, possessed by the Usurper, kills off the entire First District and destroys Miyu, the latter action sealing off the possibility of pushing the Reset Button and undoing any of the deaths.
In Horseshoes And Hand Grenades, Norio and Chosuke are trying to find the whereabouts of one Misa Torizakinote The head of the Ugly Ducklings cult that Norio was part of and who made Norio transform back into Cygnus despite the fact that Norio didn't want to and has been recently kidnapped by Gentaro for some unknown purpose only to find her body resting against a tree, gutted and obscenities written on her arms. Chosuke states it best.
Chosuke: Norio, don't look now but I think Misa just killed herself.
Earlier in that same episode, shit really goes down when a brainwashed Ryusei kills Shun, landing the first kill in the story.
The events of Kung Fu Panda 2 actually start with Shen killing Master Rhino with his cannon in order to show how evil the peacock and his wolf army actually are.
Films — Live-Action
The first 45 minutes of Audition could easily be mistaken for a romantic drama in which everything is slightly... off. Then we get Asami'sEstablishing Character Moment, which is so scary that it turns the next half hour of violence-free romance into pure terror.
The original Night of the Living Dead gets two back to back in the same sequence. First we get something that looks like this, specifically the deaths of Tom and Judy. In any other horror movie made at the time, that sequence alone would have been enough to qualify as this trope. It doesn't, but only because the real punch comes immediately afterward when we see an extremely graphic (for its day) image of the zombies chowing down on the recently charred corpses. Roger Ebert's reaction provides the page quote. It's worth emphasizing the "Darker than the audience has been led to expect" bit:
Roger Ebert:This was in a typical neighborhood theater, and the kids started filing in 15 minutes early to get good seats up front.
Gran Torino gives you one when Sue returns from the Hmong gangs brutally raped and beaten.
Million Dollar Baby is a story of a waitress who wants to improve her life: she learns how to box and manages to achieve international fame up to fighting for world title which leaves her a quadriplegic for the last third of the movie.
Unforgiven has Ned's death and Munny's return to his hard-drinking, murderous ways.
Drive shifts fairly abruptly from being a low key character study to being a Bloodier and GorierRoaring Rampage of Revenge crime story when Standard is killed. To clearly state the shift for anybody who wasn't clued in by that, the villains then proceed to splatter Blanche's brains all over the wall a few minutes later.
A Song of Ice and Fire: From the start the series is clearly darker and more cynical than the usual fantasy novel. But Ned's execution takes it to a whole new level. You do NOT expect a main character to die like this. And again when the Starks are betrayed by the Freys (the television version of this quickly became infamous as one of the biggest Gut Punches in the history of television).
As befits the title, the ending of Changes is one for The Dresden Files. Prior to Changes, the series was relatively light - while the good guys have never had it easy, they still usually came out without too many severe casualties. Then, at the end of Changes, Harry has to murder Susan to both save his daughter and completely wipe out the Red Court. He is fatally shot shortly afterwards. The subsequent books have picked up the tone shift and run with it - Ghost Story shows in painful detail exactly how much of a toll Harry's death has taken on both his friends and the world, while Cold Days involves Harry having to deal with his seemingly inevitable transformation into a sociopathic monster due to the Winter Knight mantle, is filled with revealafterreveal, and ends on an even more depressing note than Changes.
Blakes Seven has a notorious one at the end of the very first episode. The hero has been framed for child abuse by the evil government and is about to be sent to a penal colony, but his heroic Crusading Lawyer and the lawyer's girlfriend have discovered proof of the government's corruption and are about to blow everything sky-high. Then in the last-but-one scene of the episode the lawyer and his girlfriend are casually blown away by government agents. The prison ship takes off. The end.
Buffy the Vampire Slayer has at least three escalating ones over its lifetime. Season One: Flutie's death. Season Two: Angel loses his soul. Season Five: Joyce dies. If anything, season two has two moments of these back to back: the aforementioned moment where Angel's soul is lost and the moment not long after where the soulless Angel proceeds to kill Jenny Calender.
Angel, Being Buffy's spin-off, one can only expect, and there's just as much gut-punching, Season 1 Doyle sacrifices himself., Season 4 Cordelia never woke up from her coma., and finally, but most prominently Fred's slow and painful death, being hollowed by having her internal organs liquified in order for an Eldritch Abomination to take over her body.
24 mixes in two during its first season: the first is early on when Janet York is murdered by the man posing as her father and again at the finale where the season ends with Jack in tears cradling his dead wife's body.
In Downton Abbey, there's Lady Sybil's death. Series 3 is just as melodramatic as the previous two, but the graphic, gasping death scene of one of main family members, who had just become a mother and is arguably the nicest person on the show was unprecedented and shocking. William's death was noble, drawn out and sweet; Lavinia was perhaps destined to die — but Sybil's death was frantic, quick and horrifying. Never before had the show been so shocking to watch.
While The Walking Dead has always been bleak, the gut punch moments have not stopped since mid season 2 when 11 year old Sophia, who was lost in the woods, was revealed to be both dead and now a zombie. Rick is forced to gun her down while her mother screams nearby. Season 3 continues the trend with Rick's pregnant wife Lori dying from a medieval c-section birth while her 12 year old son screams and cries, he then has to shoot her dead body in the head so she won't turn into a zombie. Rick has a full blown mental break upon finding out, goes to find her body and discovers a zombie has eaten it. Rick mercilessly kills a hotheaded prison inmate in a "three strikes and you're out" situation and The Governor deliberately shoots Merle in the gut so he will turn into a zombie, shortly before his younger brother Daryl catches up to them and is forced to put down his only surviving family member.
Pretty much the entire a-plot of The Coming Of Shadows from the Emperor's heart attack onwards is a series of escalating gut punches.
The deaths of every single GROPO we just spent an episode meeting in GROPOS.
The revelation of the sleeper agent in Divided Loyalties.
The slow revelation of the truth in Passing Through Gethsemane, with one more in the tag.
Two words from The Day of the Dead: Zoe's dead.
But probably the single greatest one in the entire series: Lennier's betrayal of Sheridan in Objects at Rest.
Charmed - the episode "Charmed and Dangerous". You know things are going south when Leo is shot by a darklighter's arrow and Paige has her powers stolen too, effectively leaving Phoebe as the only sister with her powers (and she is the weakest active power-wise) with the Source of All Evil out for the kill.
The Reveal of who exactly killed Laura Palmer on Twin Peaks is one of the most infamous of these in TV history, to the point where AMC ran no commercials whatever for the final twenty minutes of the original broadcast.
Guild Wars opens in the fairly idyllic area of Ascalon - grass and flowers are everywhere, and enemies are easy and will generally not attack you unless provoked. Then the Searing happens, and you get out of the prologue.
Final Fantasy VII features the reveal of the Big Bad's plan to end all life, his successful acquisition of the MacGuffin he needs to do it, and the death of the only character with a means to stop him, all in short sequence at the end of Disc 1 of 3 (which had been largely light and partly humorous up this point except for some angst in the backstories of party members).
Tales of the Abyss starts out as a typical cliche packed Shōnen adventure. Then, about a third of the way through the game, The Reveal occurs (The main character is a replica, having been created for the express purpose of playing his original's role in fulfilling a prophecy in which he's manipulated into destroying an entire city) and we are subject to one of the most vicious examples of Break the Haughty ever seen in a game.
Yggdra Union waits until the player has been lulled into a suitable sense of security before it shows its true colors — it seems upbeat enough for a medieval war game for two thirds of the plot. Then there's Battlefield 40, where you begin your invasion of The Empire for the sake of protecting The Kingdom, and have to slaughter an entire town of civilians determined to defend their homes. And it gets worse very quickly from here.
Digital: A Love Story starts off as a simple 1980's email simulator, then the players 'go to' website crashes, and they lose all contact with Emilia. They then receive an email from the websites administrator that reveals Emilia was sending them an email desperately begging for their help before the crash and things get very dark very quickly.
ZODIAC Virgo from RefleX delivered two substantial of these. The first when it shot down Cancer from behind and the second when it destroyed the Pheonix.
World of Warcraft gives you the events of the Wrathgate. The Forsaken unleash the New Plague. You now see it cause the senseless and meaningless deaths of some of the Horde's and Alliance's greatest heroes and shatter any chance of peace between the two factions. Oh, and if you're playing as Horde, you helped createthe New Plague, in one of the more light-hearted questlines that go all the way back to the first levels.
In Mists of Pandaria, at the end of the Jade Forest questline, the battle between the Alliance and Horde, with their respective Jinyu and Hozen allies, results in the Sha being empowered, devastating the landscape and both sets of combatants.
In Mass Effect, you have a few missions trying to find out what Saren is up to, and a ton of sidequests mowing down violent criminals and terrorist cells with impunity. Then you have Virmire. No matter what you do, no matter how well you play, either Ashley or Kaidan will die. It's up to you to decide who performs the Heroic Sacrifice. You may have to put down Wrex as well, depending on your influence with him.
The Gut Punch for the series as a whole is the ending of Arrival, which requires Shepard to destroy a Batarian system killing countless innocents in order to stop the Reapers. It's essentially saying that from this point on, no matter what you do, you'll still be hurting someone.
The third gamestarts with a Gut Punch. A front-row seat for the Reaper invasion of Earth. There's also the fall of Thessia, which is a complete and utter defeat for the good guys, which, in an earlier version, would have included a Virmire-like dilemma.
Live A Live appears to be a collection of fairly cheerful Cliché Storm tales of heroism. Then you finish all seven and unlock an additional chapter, which seems to be a standard Sword and Sorcery tale... until Oersted is tricked into murdering the king. Everything in his life falls apart from there. Ladies and gentlemen, the origin of Odio.
Baten Kaitos: The Mole is unmasked. It's Kalas. The main character. He's led you - not just you the player, you the player stand-in Guardian Spirit along the entire time. And then he cuts off your viewpoint and the screen fades to black. Oh, by the way? The really nice leader everyone loves? She's pure evil, and the one he's working for. And that's when you realize you've judged the entire plot the wrong way from the minute you hit Start.
The gut punch in Metal Gear Solid 2: Sons of Liberty is the point where the President of the United States confesses that he's just a figurehead for an Ancient Conspiracy, that the entire facility the game is taking place on is a cover for a massive new battleship with vast nuclear strength and weapons to control information, that you're just a pawn of said ancient conspiracy, and that he wants you to kill him (which someone else beats you to). The whole scene sets the tonefor the restof the game, and to an extent the series.
Spec Ops: The Line initially comes across as a shooter with a somewhat darker-than-usual undertone, when it becomes apparent the situation is not one suited for your tiny rescue and reconnaissance squad. About halfway into the game, Capt. Martin Walker uses white-phosphorus mortar rounds to pass an enemy camp, only for the game to reveal the resulting gruesome murders included forty-seven of the civilians he's there to rescue. The game and Walker's mental stability only go downhill from there.
BioShock has the infamous scene in Andrew Ryan's office, in which the true nature of the game finally rears its ugly head. It is revealed in short order that not only has Atlas had you on puppet strings for the full duration of the game, but he's really Frank Fontaine, the one responsible for much of what's happened to turn Rapture into the Crapsack World that it is. And by the way? You Have Outlived Your Usefulness.
Homeworld pulls this off very effectively in Mission 3, where you return to Kharak after a short test jump to discover that the planet's surface and orbital installations have been destroyed, effectively rendering the Kushan species near-extinct. The narrators in particular help the scene by just barely maintaining a calm and collected tone.
Dark Souls sets itself up with an especially bleak Dark Fantasy setting from the get go, which makes the subdued, sudden and un-dramatic NPC deaths (typically at your hands following their turning Hollow) gradually easier to deal with, except for Solaire's descent into madness and despair. The fact that the majority of players would not know that it was avoidable until later adds to it.
Homestuck is pretty light material... right up until Jack Noir flips the fuck out and goes on a homicidal rampage, instantly promoting himself to Big Bad.
This also very suddenly demonstrates the darker turn the comic takes in Act 5 Act 2. (Spoilers in link) Despite the fact that he gets better, the main character dies onscreen with basically no warning right after a particularly lighthearted and charming sequence, and the girl who led him there responds with a smiling emoticon.
The Order of the Stick: Due to Xykon's Laughably Evil tendencies, it's very easy to assume that he's not that much of a threat. However, during the invasion of Azure City, he swiftly reminds the audience exactly how dangerous he is by KILLING ROY.. and then Tarquin kills his own son, Nale.
Avatar The Last Airbender has an unusually late example at the end of season 2. Up until that point, the show had proven its willingness to tackle difficult subjects, but always ultimately ended in a relatively lighthearted way. In the season two finale, despite a great deal of foreshadowing Zuko refuses to take a Heel-Face Turn and instead sides with Azula, the Fire Nation succeeds in taking over Ba Sing Se, held up as the Earth Kingdom's last defence, and just when a Hope Spot arrives in the form of Aang reaching the Avatar State, Azula attacks him mid-transformation, outright killing him, his life only spared by the magical water Katara had received from the northern water tribe. Where Season 1 ends with the heroes victorious, season 2 ends with them battered and broken and having lost much that they had gained.