Captain Joe: (pensive) We don't deserve half the things we get. (laughs maniacally, then throws down his pen angrily) You're stuck here!
Almost each episode of Cold Case starts as such. There is at first a relatively happy scene with the victim and his/her family or friends, which brutaly ends with the dead corpse of the victim, and police agents who close the investigation file...
The Pilot episode of LOST has a good example of this trope. About mid-way through the two-hour series opener, the Losties get the radio from their plane working and hear a transmission in French. After a couple seconds of them cheering that the French are coming to rescue them, Shannon translates the transmission which says in part: "I'm alone, all alone the others are dead." The Mood Whiplash makes a creepy moment far more terrifying than it already would be, and this moment basically sets the tone for the entire series.
Possibly the most chilling moment in this show's history: in the season one finale, they're on the raft, they fire the flare—and suddenly there's a light! There's a boat! There's triumph music! They're saved! And then: "Only the thing is, we're gonna have to take the boy." HOLY CRAP.
A particularly heartbraking one is the episode where Claire sucessfully delivers her baby, and Sayid surprises Shannon with a romantic dinner. All this at the same time Jack is trying (and failing to) save Boone's (Shannon's half-brother) life. The final scene shows people gathering happily in the beach to tell the good news, then we see Shannon and Sayid also arriving and the look on Jack's face when he sees them.
On a similar note, the soundtrack for this show. A prime example is "Life & Death": the first three minutes are a tearjerking meditation on well, life and death, and the last thirty seconds is you being dragged into hell.
The Vampire Diaries has this when Vicki, after dancing and partying it up after Damon heals her, has a breakdown and starts crying about how awful her life is. Damon's response is to snap her neck (she gets better).
He almost did it to Caroline too but Elena prevented him.
In the season four finale, Stefan says his final goodbye to Lexi's ghost and starts planning which city to visit during the summer, finally resolving to try to get over Elena... and then Silas sneaks on him, locks him in a safe and throws him in the river.
There was also that time in season one when Bonnie and her grandmother were able to open the old grave just in time for Damon and Stefan to get out, and for Anna to rescue her mother Pearl. Elena and Bonnie go home victorious... and suddenly Bonnie's grandmother drops dead out of the exhaustion of the spell, which marked Bonnie's start to more powerful and dangerous magic.
Wizards of Waverly Place is a lighthearted teenage comedy without any serious consquences for anyone for years until suddenly Justin's very old vampire girlfriend ages to her real age and Alex's boyfriend turns out to be a jerkass and is turned permanently into a wolf.
Chuck s 2nd season had "Chuck vs. Santa Clause", a hilarious homage and parody to Die Hard, with nearly every scene being a funny reference to the movie. At the end, the day is saved ... and Chuck secretly watches Sarah execute the unarmed villain in cold blood, and then coolly lie to his face about it. Anna and Morgan are also on the outs.
Supernatural had goofy, self-referential episodes right in the middle of incredibly dark and bleak arcs. Season Two and Three are the guiltiest of this.
Forgetting certain episodes for a second, the basic premise and the actual tone jar together so much that it makes the show the western king of Mood Whiplash. Because, honestly, would you believe that a show that has the premise of two brothers hunting down demons with rock salt could be one of the most unbelievably downerish shows around?
Supernatural also had a case of internal Mood Whiplash in the episode "Mystery Spot." The episode starts out like a normal "Groundhog Day" Loop episode in which the same Tuesday plays over and over again, with only Sam experiencing the loop; the trigger for him to start the day again is Dean's violent and unpredictable death. Despite the dark subject matter, however, the first half of the episode plays like your standard goofy comedy installment - wacky montages, upbeat music, constant one-liners and jokes; until Sam figures out the Trickster is behind it, convinces him to end the loop, and Dean dies for real. Then the episode transitions into a incredibly dark months-long journey with an emotionally destroyed Sam hunting the Trickster until he finally lays hands on him. In the end, everything is reversed, but Sam is just a little more unstable.
Simon Said had this in spades. It starts with Sam having one of his painful death!visions, then Ash comes in for some comic relief and Dean sings REO Speedwagon, then Sam angsts some more and someone gets killed, then they find Andy's "Moby Dick Bong", then Dean gets mind-fucked (for the second time) into admitting he's scared for Sam and Sam has another death!vision, then Evil!Twin humor and then full-blown angst with Tracy's Mind Rape, seriously-painful-in-hindsight foreshadowing of Dean's wish for death (he gets forced by Webber to put a gun to his head), more Sam!Angst and a not-so-nice twist in the "psychic-kids" storyline.
We can't forget episodes like Wishful Thinking, where we go from hilarity like a suicidal, alcoholic teddy bear and "KNEEL BEFORE TODD!" to Dean's confession that he remembers every detail of what happened to him while in Hell.
Or Yellow Fever, where we start out with Dean running for his life from a tiny little yappy dog, and end with Dean terrified, about to die, confronted by Lilith again, and seeing Sam as a demon. Yeah.
Or Changing Channels, with the boys trapped in Grey's Anatomy and a Japanese game show, ending with Gabriel's heartbreaking reveal.
Or Hunteri Heroici, which plays with every Looney Tunes trope there is, has Castiel join the brothers on a hunt and provide hilarious one-liners... and Cas admitting that if he sees what he did to Heaven, he's scared he'll kill himself.
Or basically any episode of the show ever. Oh Show, you're a manic-depressive but we love you anyway.
Scrubs features this rather prominently, being a comedy set in a hospital where people have a tendency to die occasionally.
The most egregious example must surely be: a pregnant couple find out that it is likely either the mother will die and their baby will live or vice versa, when the show suddenly cuts to J.D.'s fantasy that they are on Candid Camera, complete with laughter and pointing at the show's actual camera before cutting back to dealing with the dilemma. Mood Whiplash so strong you'll be massaging your neck for hours.
Don't forget the one where, upon learning (in the first 10 minutes of the show) that a patient has terminal cancer, JD imagines the rest of the episode as a wacky TV comedy. It turns out they got the results wrong, and the patient who actually has cancer "is anti-semitic, so no one cares". Cue laughs. Oh, what is that strange beeping sound? Oh yeah, back to reality again, with the cancer patient losing consciouness.
It's a whacky musical episode with songs about guy love written by the people who made Avenue Q! Oh by the way, there's a brain aneurysm too.
How about "My Screw Up": Dr. Cox is joking with Ben as they're walking towards Jack's birthday, when an obviously perturbed JD walks up to them:
"My Lunch" has a beyond-cruel one, cutting from The Reveal that Todd was just pretending to be gay so he could check out Elliott and Carla to JD and Cox trying and failing to save their rabies-infected transplant patients.
An episode centres around Cox telling Jack a fairytale story that is really the story of JD trying to find out what's wrong with a patient. After he leaves the room, Jordan eagerly asks if the patient was okay, only for Cox to reply that that's the way he's telling it.
Firefly has a tendency to quickly and unexpectedly shift from intense action to engaging drama to heart-wrenching sadness to laugh-out-loud hilarity to warm and fuzzy, within the space of a single episode.
The "He is psychotic!" scene in the pilot is particularly epic.
It's even got an example of a character getting the brunt of the whiplash. River is dancing, actually happy for once, while the others are having a wild west shootout, unbeknownst to her. Then Shepherd Book is wounded, and both the audience and River have the same reaction.
On Angel, the writers would frequently place an amusing or lighter-hearted episode before starting a dark story arc. More memorable episodes include the ballet episode that aired before the "Father will kill the Son" arc and the seriously amusing "Smile Time" which aired before the Fred/Illyria episode.
Specifically, she has just had a whole battery of tests, all of which say she's fine. She starts to sing "You are my sunshine" to Wesley, Lorne whirls around with a look of complete horror, and she starts coughing up blood.
After the Darker and Edgier second season plot arc of "Darla and Angel", the creative team indulged in a whimsical 3-part season ender, set in a fairytale kingdom, to deliberately offset the grimness of preceding episodes.
And then at the end of that arc, Angel returns to earth and gets the news that Buffy died while he was away.
Let's not forget that this was also repeated in "You're Welcome", where after the day is won and everyone is celebrating, Cordy and Angel have one last kiss. She says, "You're welcome.", the phone rings, and Angel finds out she died that morning. Let the tears commence!
"Spin the Bottle" which is Angel's equivalent of Buffy's "Tabula Rasa" is a perfect example of this. The majority of the episode has the Angel Investigations crew all having their memories regressed to their teenage years and all sorts of wacky hijinx going on: Wesley returns to his wussy self from Buffy's third season, Fred is revealed to have been a pothead as a teenager, Angel's memories go back to before he even became a vampire and he mistakes a group of cars for demons... and then the end happens where everyone gets their memories restored. we get our first glimpse of the first major antagonist for the season, Cordelia leaves the group and Angel is alone and heart-broken, and Lorne, who's also been directly addressing the audience the whole episode closes things out by delivering one of the most somber, heart-breaking monologues on television.
The episode "The Magic Bullet" begins with The Beach Boys playing as complete strangers share the love of Jasmine. A commuter happily stops his car to allow some pedestrians to cross — only for a wide-eyed Fred to slam into his window before fleeing, pursued by Wes and Gunn.
Buffy is rife with examples. Oh, where to start... could it be with the part in Innocence where it goes from passionate love story to "zomg, Angel is EVIL!"? Or how about season six, where it went from a musical episode to a magical addiction fueled angst-fest?
The Puppet Show has one in-universe mentioned by Cordelia. In the talent show, her song about 'dignity, and human feeling, and personal... hygiene, or something like that' is set up to occur just after a band's rock song. She says something along the lines of, "The point is, my song is sappy, and no-one is going to feel sappy after all that rock and roll?" Giles quickly makes her go away by mentioning her hair.
Once More with Feeling contains an enormous one in addition to all the song-specific ones listed below. The episode begins with cheery singing and dancing and fabulous songs and end with the main character's attempting suicide! And then it ends with a kiss...
Or "Tabula Rasa", with its 37 minutes of madcap memory-loss hilarity (including a kiss between Anya and Giles) followed by Giles going back to England and Tara leaving Willow. Only episode of television that has EVER had me literally laughing one minute and crying the next. Very well done, though.
Or how about the zany madcap jaunt about a geek and his robot girlfriend that ends with Buffy finding her mother's dead body? And then, of course, the geek turns out to be the bastard son of Lex Luthor and Max Cady.
Even without Joyce's death, "I Was Made to Love You" is still pretty whiplashy - like the part where April nearly kills Katrina after the latter "lies" about being Warren's current girlfriend, or when she "dies", still believing that Warren would come back to her.
Everything to do with the Geek Trio in Season Six has Whiplash. Just one example is in "Dead Things," when they start with a zany plan to acquire a sex slave then accidentally murder her and try to frame Buffy for it.
Storyteller is pretty much pure comedy (One scene features Andrew narrating the story of Faith fighting Spock). Then they get to the seal, and Buffy threatens to kill Andrew:
Buffy: When your blood pours, it might save the whole world. What do you think about that? Does it buy it all back? Are you redeemed?
Andrew: No. Because... I killed him. Because I listened to Warren and I wanted to believe it was him, but I knew it wasn't. So I killed him, and now you're gonna kill me, and... this is what Jonathan felt. (he starts to cry)
"End of Days" has a serious dialogue where Buffy and Faith contemplate the loneliness of being a Slayer ending with the following line:
Faith: Thank God we're hot chicks with superpowers.
Or how about "Standing", Giles' song from "Once More, With Feeling", in which he realizes that he must leave Buffy so she'll learn to stand on her own? He sings as he watches Buffy going through her exercises, and as the song ends, she walks up to him, unaware of what just happened, and:
Buffy: Did you just say something?
Or in Selfless where we go from Anya singing about how she'll be Xander's Missus, to her impaled upon Buffy's sword? (She gets better)
Episode placement will do it too...right in the middle of the 'Angel goes bad' arc we get a wacky story of Xander casting a love spell - then back to the pain and angst.
In the Season One finale, the Master is hamming it up during an earthquake. After the shaking stops, he turns to the Anoited One and asks:
The Master: What do you think? 5.1?
Or (told you Joss loved these), the whole ending scene of "Bad Girls", where the Mayor goes through the ritual to become invulnerable.
Mayor: [very deadpan] This officially commences the Hundred Days. Nothing can harm me, until the Ascension... [breaks into giggles] Gosh, I'm feeling chipper! Who's for a root beer!
An unintentional example occurs in "The Body": the episode has no score, which adds to the harsh realism of an emotionally devastating story. Except nobody bothered to remove the loud, upbeat theme song from the end credits. It's somewhat jarring.
Another good example is the episode "Seeing Red" from season 6. Willow and Tara finally get back together after being apart for pretty much the entire season and are shown incredibly happy for the whole episode. Amber Benson (Tara's actress) finally gets to be in the opening credits, too! Everything's going great... then Warren kills Tara.
The Wish offers a good one - the alternate Sunnydale is ruled by vampires, the Master's still alive and kicking and now factory processing humans, and just about every main character dies. And then Giles undoes the wish and we're back to Cordelia, who'd died around the halfway point and was the one who made the wish, gleefully rattling off a series of wishes of what horrible fate should fall on Buffy, Xander, and Willow, and eventually all men while Buffy, Xander, and Willow cheerfully chat in the sunlight.
There's a pretty good moment that fits this trope well in the third season episode "Helpless." After learning that Giles is responsible for her temporarily losing her Slayer powers, Buffy directly confronts her mentor over his betrayal of her trust. The scene gets more and more dramatic as Buffy becomes more horrified and Giles tries to do anything he can to make it up to her, and then suddenly at the end Cordelia comes in completely oblivious as to what's going on. As Buffy coldy tells Giles, "I don't know you," Cordy takes her literally and believes some demon has given her amnesia, as well as wondering from their serious expressions if the world's supposed to end again and whether or not she should bother studying for an exam if that's the case.
In Season 9, Whistler, after inviting Angel out for dinner to talk, punches a hole through his stomach. After almost killing him, Whistler decides to spare Angel then tells him that once his stomach grows back, he should try the food there.
Xander tells Buffy, "When I'm alone against the dark, I think 'What would Buffy do?' You're my hero. ...And sometimes when I'm alone in the dark, I think 'What is Buffy wearing?'".
In "Omega", Echo's line upon arriving at Alpha's lair:
Echo: Say, you got a bathroom?
Episode 2.11, Getting Closer: Topher and Bennett's kiss scene, which leaves them both giddily happy; it manages to be both Crowning Moments of Heartwarming and Funny alike. Topher steps out for a minute and Claire walks in to have a conversation with Bennett that does nothing to lessen the charming atmosphere. Then Topher comes back and Claire immediately pulls out a gun and blasts Bennett's brains all over him.
Ashes to Ashes has a lot of this. The season 1 finale in particular goes from farcical to heartwarming to OH SHIT in the space of about fifteen minutes.
The last 10 minutes of the Season 1 finale of Queer as Folk (US). Commitment-phobic Brian shows up at Justin's prom, where the two share an epic Dance of Romance and even a Big Damn Kiss in front of everyone. Then they're leaving to continue their romantic evening when Justin gets gay-bashed with a baseball bat to the head and the season ends with Michael coming to Brian in the hospital waiting room, Brian looking utterly broken with Justin's blood staining his scarf. Wow.
Misfits has this on its' very first episode: we have Alisha recounting to the boys how she got pulled over by a cop for driving drunk and tried to avoid it, which includes a lot of sensual licking and sucking of a water bottle (the guys' reactions, Simon in particular, are ''hilarious''), while at the same time Kelly is running for her life as a Brainwashed and Crazy Tony attempts to kill her. One story inerrupts the other time and time again, and when Kelly gets to the bullding the rest of the group is in it's when the episode turns 100% serious.
In a bizarre case where it's used for comedic effect, the old UK sketch show Not the Nine O'Clock News where two politicians are in a shouting match until one of them drops dead on the stage, resulting in a line to the effect of: "How can you believe these lies! This man... * URK* ...will be sadly missed, and our condolences to his family."
"The Chase" is mostly a ridiculous comedy with Slapstick and a Comic Trio of Daleks who don't seem all that threatening. The atmosphere is very loopy and comfortable. Then Ian and Barbara, two very, very loved companions who'd been there since the beginning of the series, realise they can use the Daleks' time-ship to return to their home time and inform the Doctor they're leaving, and he snaps at them both out of selfish grief.
In "The Green Death", after the menace has been destroyed, the Doctor's companion announces she is going to leave the Doctor and UNIT to get married and explore the Amazon. There are smiles and congratulations all round, even from the Doctor. But when the companion walks away to talk to someone else, the Doctor sadly downs his drink, leaves quietly, and drives off alone.
The revival series embraces this trope wholeheartedly whenever it would cause the Doctor the most angst. See "Journey's End", which has triumph, reunion and celebration followed by the Doctor being forced to Mind Rape one of his companions to prevent her from dying and being all alone again as a result. The whiplash actually occurs in mid-scene, as Donna is babbling her newfound Time Lord knowledge in a rapidfire manner and just generally being hilarious as the Doctor starts to look sadder and sadder, and then, in mid babble, Donna starts to repeat the same word over and over in a stuck-record fashion and you start to realize that something is very very not right.
An example in the preceding episode "The Stolen Earth" is the beautiful reunion scene where the Doctor and Rose notice each other and start running into each other's arms when suddenly, out of the blue, a Dalek rolls up and shoots the Doctor.
The end of The End of Time: Tearily, after tying up loose ends with Martha, Jack, Sarah Jane, Donna's family, and saying hi one last time to this universe's Rose: "I don't want to go!" One regeneration-plosion later: "I'm a girl! No! No! I'm not a girl!"
Part of what makes the above scene so drastic in mood is that not only to we switch Doctors, and their behavior is utterly different, but the music changes with them. Ten's final song is Vale Decem, and it's a good-bye song from the universe to him, very sad and tragic. Then, Eleven leaps onto the picture, and the music is drastically different, a rock-and-roll, jumpy, energetic beat that you could dance to.
A few of the regenerations could count as this, as we're basically witnessing a death and a birth at the exact same time. For this reason they typically take place right at the end or beginning of an episode/serial, as it means they can start fresh and avoid this trope. But other good examples of Whiplash would be Five's regeneration into Six (we go from his hallucinatory death scene right to Six snarking at Peri) and Nine's regeneration into Ten (his tearful goodbye to Rose right into a joke about having "new teeth").
"Doomsday" goes from a tearful farewell between Rose and the Doctor to the Doctor and Donna, wearing a bridal gown, shouting "What?!" at each other at increasing volume when she suddenly appears in the TARDIS.
The episode before, "Army of Ghosts," had a very large mood whiplash as well, with the Doctor being told by the Cybermen that "The Sphere is not ours." It was made by the Daleks, so the whiplash is from "This is bad," to "We're all gonna die."
Amy Pond goes through one herself in "Cold Blood" her fiancé Rory is killed, causing her to become inconsolable from grief. But then he is absorbed by the time-absorby-lightpasta-thing and he is made to have never existed, so she doesn't remember him or his death, leading to her cheerfully continuing despite the huge loss which just happened (or not). It's disconcerting, to say the least.
"The Big Bang" does this so much, it'll leave your head spinning that is, if your head isn't already spinning from all the timey-wimey bits. Seriously, the episode starts with the universe in shambles and Rory holding Amy's body, begging her to laugh, when the Doctor pops out of midair holding a mop and wearing a fez. He pops in and out three times while explaining that Amy is actually not entirely dead, it's the end of the universe, and Rory needs to go down to the Pandorica to let the Doctor out. The rest of the episode consists of the Doctor getting killed in the future, the TARDIS exploding with River in it, River getting rescued, more fez jokes, the Doctor getting killed, the Doctor actually not being dead, but he's going to be erased from time instead, the actual process of being erased from time, and then the Doctor gets unerased from time, and gets to come to Amy's wedding and dance really extremely badly. It's hard work, this show is.
Also, in "Partners in Crime", when Donna and the Doctor are both chasing the head of Adipose and her hostage. Donna is watching through the door window, and the Doctor is watching through the window in the wall across from the door. There's a very serious questioning going on. Then the Doctor and Donna catch sight of each other. Hilarity Ensues. Then, mid-word, Donna realizes that they've been noticed. Cue chase scene.
"The Doctor's Wife" cuts from the Doctor in tears (and Amy and Rory nearly so) as the TARDIS loses her human form, to the Doctor working on the TARDIS's machinery, chatting with Amy and Rory about bunk beds, and asking the ship, "What do you think, dear? Where should we take the kids this time?"
Despite being somewhat dark, "The Almost People" wraps things up on a fairly hopeful note... and then the Doctor unexpectedly melts Amy into a pile of goo, and she wakes up in prison about to give birth...
"A Good Man Goes to War", the mid-series finale, ends with (among other things) everyone finally learning just who River is. Cut to a card telling us the Doctor will return in Autumn with "LET'S KILL HITLER."
In "The God Complex" not only do the viewers experience it at every turn but so do the characters when they are possessed.
In "The Sound of Drums", we cut from The Doctor, Martha, and Jack running down an alleyway to televised news reports about the first contact with the Toclafane to... the Master watching the Teletubbies, which he marvels at the concept of television "in their stomachs".
Even better, right before the Teletubbies, we had "This is Gallifrey: Our Childhood, Our Home" playing in the background. And then, bluegrass-type music.
The Angels Take Manhattan... hooBOY! Rory has decided to jump off the hotel to kill himself and create a paradox that will ruin the Weeping Angels' food supply, and Amy decides to go with him, not being able to bear to live without him. The paradox resets the events of the story, taking them all back to present day New York, ready to embark with The Doctor and River on a family voyage. Rory, however, gets distracted by his own gravestone and is transported back to 1938 by a surviving Angel. Despondent, Amy allows herself to be sent back with him, leaving the Doctor and River helpless to save them.
We get this treatment at the end of "The Time of the Doctor". It goes from the Eleventh Doctor quietly accepting his death and seeing Amy one last time to a very quick regeneration to a disoriented Twelfth Doctor babbling about his kidneys and forgetting how to fly the TARDIS.
Torchwood is not without its own Mood Whiplash. The most blatant comes from the season of Torchwood: Miracle Day, where a scene goes from nostalgic-romatic, to comedy, to angst, all in the same scene and within the space of a few minutes.
Tonight, on a very special episode of Popular, Harrison must resolve his mixed feelings about his mother when his friends discover that she's gay...
...and Mary Cherry chains Gwyneth Paltrow's personal shopper to a pipe in the school boiler room.
Rescue Me thrives on this trope. One minute you'll be rolling on the floor at the various antics of the guys of 62 Truck, two seconds later a bunch of kids die horribly in a fire. Pretty much every episode is like that.
The Burn Notice Season Four episode "Friends and Enemies" is mostly lighthearted at first, with the week's client (a spy that Mike accidentally burned) being introduced to the trio's dynamic and making lighthearted banter. The villain is even defeated by having the police catch him with guns in his trunk—a trunk that snaps open dramatically two moments, after the car flips, spilling the guns all over the street. Then cut to the next day, to where the not-arrested-after-all villain is horrifically torturing the client for information...
Battlestar Galactica - "Sometimes a Great Notion": after discovering that Earth is a radioactive wasteland Dualla cheerfully reconciles with her estranged husband then puts a bullet in her brain.
Blackadder - The finale of the fourth series suddenly takes an abrupt swerve out of comedy territory in the final five minutes. The entire final episode features Blackadder once again attempting to get out of "The Big Push", that is, everyone in the trenches entering No-Man's Land assaulting the German front. In previous episodes, he and the other characters have gotten out of these assaults, but at the end of this episode he realises that there's no way to get out of it this time, and he, George, Baldrick and unexpectedly Darling, end up going over the top with everyone else, Blackadder's last words before going over being "Good luck, everyone". All of them are killed within seconds of going over, and the final, silent shot of the series is of an empty field of poppies in spring. There are no jokes in these last few minutes whatsoever, it's entirely dramatic, and in a comedy series, this comes as being a very unexpected Tearjerker.
A specific example of a beautifully-executed mid-sentence Mood Whiplash in this episode comes when Captain Darling, about to go "over the top" to his likely death, is listing all the things he'd hoped to do when the war ended. "Go back to work at Pratt and Sons" gets an audience laugh, as does "Keeep wicket for the Croyden gentlemen", but these are followed by a brief pause and a wistful "Marry Doris". A character who'd been portrayed as just a petty comic foil to Blackadder up to that point suddenly gets humanised.
Darling: Made a note in my diary on the way here. Simply says..."bugger".
George gets a very similar mid-sentence whiplash.
George: Well really this is brave and splendid and noble...[pause]...sir?
Blackadder: Yes, lieutenant?
George: I'm scared, sir.
There are jokes right up until Blackadder's penultimate line, but they are all extremely grim. It's called Trench Humour for a reason.
And of course that moment moments before the end where they are lined up ready to go over the top, artillery booming in the background, when... silence falls.
Darling: Listen - our guns have stopped.
George: You don't think...
Baldrick: Maybe the war's over. Maybe it's peace!
You actually start to feel hopeful for the characters that fate has intervened and they have escaped certain death, and then Darling says...
Darling: Thank God! We lived through it! The Great War, 1914 to 1917!
...And we know that the First World War actually ended in 1918.
That Mitchell and Webb Look referenced the famous Blackadder example above in the fourth series's penultimate episode, joking that they would follow suit and see the show off dramatically. Fast forward to the last sketch of the series a week later, in which Dr. Watson visits a dementia-riddled Sherlock Holmes and through a very silly exchange allows him to think he's still the cleverest mind in England. Then, Holmes has a moment of clarity.
Holmes: I know, John. I do know. I just... can't get the fog to clear.
The Hogan's Heroes episode "Operation Briefcase" was surprisingly dark, featuring an agent actually dying (offscreen) while in Hogan's care, when most involved escapes by the skins of their teeth. Even more unpleasantly, this episode dealt with an attempt to assassinate Hitler—an attempt, as everyone should know, that failed.
In the Batman Cold Open of another episode, the guys are meeting an Underground agent who was a female impersonator before the war. Jokes fly, then Germans crash the meeting, fire at the good guys and take off in pursuit of the Underground agent. Hogan and his men get up again, Newkirk cracks a joke at the expense of the French... and they realise that LeBeau is still on the ground and has actually been shot. Cue one of the most dramatic moments in the (usually) comedic series when Newkirk does a 180 from his usual Deadpan Snarker persona and says quietly, "Colonel, my little mate's been hit."
Stargate SG-1's most prominent comedy episode "Window of Opportunity" ends with one of these. The episode's all wacky time-loop fun until we find out why the archeologist is looping time; he's trying to bring his dead wife back to life, which of course leads to an outburst from the usually jovial O'Neill:
O'Neill: Listen to me... I know what it's like.
Malikai: YOU CAN'T!
O'Neill: I LOST MY SON! I KNOW!
The end of the Stargate Universe episode "Light". The mood the entire episode has been one of resignation. Then Rush realizes that they're all going to live, and the mood shifts to elation. Then they realize that Destiny is accelerating too fast for the shuttle to catch them, and the mood shifts again to action, as the crew work together to get the shuttle back home.
Power Rangers RPM. Jesus. For a season that has unquestionably the darkest plot Power Rangers has ever done, this series also seems to have some of the most off-the-wall humour. Highlights include Ranger Green attempting to use his teleportation ability, only to teleport his suit, leaving him in his helmet and underwear, Ranger Green getting a wedgie from a disembodied robot hand, Ranger Green fumbling his one liners, Ranger Green... y'know what? I think you get the idea.
Likewise with Dr K. At first she just seems a little strange and kinda funny, being protective about the ranger tech and even wearing bunny slippers in one episode. Though all urges to laugh at her behaviour suddenly go away when you think of her back story...
On Deep Space 9, "The Magnificent Ferengi" bounced back and forth between ridiculous and awesome repeatedly. Especially evident in the end, when Quark's team has just beaten the remaining Jem'hadar in a shoot-out and captured their Vorta leader, the triumphant mood is suddenly turned hilarious by showing the dead Vorta (reanimated with carefully-controlled electrical impulses) trying to walk into a wall, with Nog saying "I can't turn him off!"
Night Court did this from time to time, often going all the way around back to funny in the same scene. In "Leon, We Hadly Knew Ye" Judge Harry's foster son (and recurring character) Leon successfully runs away when he can't stand his nice, but prudish new adoptive parents. He's not seen again for the rest of the season. "The Hurricane: part 2" goes all the way back around to funny again. After helping deliver the babies of four couples during a thunderstorm and blackouts Harry slips away to have a deep and emotional talk with God in front of a cross someone left in the courtroom.
Harry: (speaking to God) You remember that one guy? Of course you do, you remember everything. I tell ya, that one shook my faith to the CORE. Then you drop this brand new life, right into my hands... But if I could just have the answers to a couple of questions, like if you've always been here than where did you come from? And does man have the capacity to rid himself of his own evil? And why IS the sky blue anyway? Well, maybe I can look that one up. But all this baby stuff... that's no accident, after all you gave us Mozart, Van Gogh, Confucius, and LARRY BIRD!" * pulls a basketball from under his robes and tosses it through a hoop nailed on the cross*
Notably one episode where Mason has to pose as a clown at a kid's party and it's hilariously cranky the entire time. Then it comes the time to collect the soul of the birthday girl's father.
Sesame Street, when dealing with the death of Mister Hooper. The scene where Big Bird shows his drawings of his friends to the adults is light and cute ... up until the point where Big Bird says he wants to show Mr. Hooper the drawing he made of him. The mood then turns changes abruptly as the adults have to explain to Big Bird that Mr. Hooper has died and he won't be coming back.
Tokusou Sentai Dekaranger had one episode where the Blue Ranger had to kill his girlfriend's little brother because he was killing women to cure his sister's fatal disease... Which she was already getting better from in the first place. The scene ends with him watching his girl cry over her brother (in a rubber monster costume) in the rain with this sad whistling song... And then you get a neck sprain from the series' usual jazzy nightclub-ish end theme.
Band of Brothers did this with episode to episode continuity. The last two episodes go from finding a Nazi concentration camp to them going into Hitler's summer home and hilariously looting it of everything of value (up to and including the photo album of his summer vacations).
The "Polar Special" on Top Gear, in which the three presenters attempt to reach the North Pole, two by truck and one with a dogsled, is out of tone with the light and rather silly stunts the gang usually pulls, sometimes jarringly. The danger involved and the fear and discomfort of the presenters is simply too real to be played for humor.
Also the episode where they paint their cars with messages as offensive to Southern Americans as possible (pro-gay, anti-Nascar, etc.) and try to drive through Alabama without getting murdered by those wacky rednecks. It's all played for laughs until they hit New Orleans and see the devastation caused by Hurricane Katrina.
That entire thing is whiplash after whiplash. First it's funny, then it gets really creepy considering those rednecks were probably very serious, followed by the very serious "we shouldn't make jokes around here" air in New Orleans. Followed by a Crowning Moment of Heartwarming by giving away their cars (as opposed to selling them for a bit of a laugh).
Right after Tom Cruise and Cameron Diaz both beat the record for 'Star in a reasonably-priced car', James May segues (complete with lampshading of the mood change) into a 15 minute piece on Ayrton Senna, who would have turned 50 that year.
The BBC Adaptation of Cranford can be quite frankly emotionally exhausting to watch. Funny and witty one moment, heart-breaking the next. Then melancholy. Then heart-warming. Then...you get the picture.
NewsRadio tried this with the episode dedicated to Phil Hartman's death by inserting jokes to lighten the mood. It didn't work too well; the real-life tears from the cast were too overwhelming for much of the episode to be really funny.
One episode of Bones ends with Brennan singing "Girls Just Wanna Have Fun" in a bar. Everyone's having fun until Pam shows up and shoots Booth.
In "Two Bodies In the Lab", Booth insists on staying with Brennan in her apartment after someone shot at her. At one point he notices a Foreigner CD in her music collection, and Booth and Brennan start rocking out to "Hot Blooded". Shortly after, Booth offers to get Brennan a beer. Just as he opens the refrigerator, he ends up getting the brunt of an explosion from a booby-trapped door.
The trope is also invoked in the episode "The Hole in the Heart", in this conversation between Brennan and Angela:
In "The Patriot in Purgatory", Brennan was inspired by watching a basketball game with Booth to bring several of the interns together for a "team building exercise", instructing them to identify as many unnamed bodies as they can. This quickly got derailed when Vasiri realized that the body he was identifying was a homeless veteran who was standing outside the Pentagon during the terrorist attacks of September 11, 2001. By the end of the episode, the team determined that he died from injuries sustained when he pulled people from the debris, saving their lives. Booth delivered his eulogy as he was buried at Arlington Cemetery with full honors.
In the final episode of season two of Robin Hood Marian was brutally stabbed to death by Guy and buried miles from home. The first episode of season three dealt the raw and bloody emotional aftermath of this. But the next episode involves Robin laughing his head off as he hang-glides from the parapets of Nottingham Castle, and Marian was only mentioned a handful of times throughout the rest of the season.
Farscape manages to do this so-often that you would swear the entire show was bipolar. Prime example, in the episode "Revenging Angel" where John gets knocked unconscious due to a comedic accident... cue Harvey appearing in his coma-hallucination telling him that he's dying... cue John turning his entire reality into a Looney Tunes world... cue slap-stick and John asking all the main characters in his head how he should survive... cue his entire world blowing up and him flatlining. This is a one-episode example. Often the show will jump from the serious arc plotline with horrific and damaging psychological implications for the characters to good old harmless space opera fun in a very short amount of time. Admittedly the show is made of Crazy Awesome but there is a heavy emphasis on the crazy.
Skins did this one in series 4; sandwiched between Freddie's Episode 5 (which ends with Effy slitting her wrists) and Effy's Episode 7 (which ends with Freddie being murdered with a baseball bat by Effy's psychiatrist), is JJ's episode, which is an almost too saccharine love story (in which JJ gets together with a colleague at the confectionery wholesalers where he works). It sticks out like a sore thumb, doesn't advance most of the other arcs of the series, and is suspected by some to exist primarily because of Executive Meddling.
Babylon 5 has a lot this. J. Michael Straczynski has gone on record saying something to the effect of "I just love giving viewers a nice, happy scene, and them slamming them on the back of the head with a 2x4." He especially liked doing this as the introduction to a Wham Episode; making the episode look like a light walk in the park, then suddenly flinging you into the Myth Arc at breakneck speed.
True Life has this, an episode about drug use may be followed by an episode about summer flings.
In the Star Trek: The Original Series episode "The Ultimate Computer", a malfunctioning computer controlling the Enterprise manages to kill several hundred crewmen aboard the other Federation ships engaging it in a mock exercise. No more than a minute of screen-time after the situation is resolved, Kirk struts back to his captain's chair and plops down with a massive grin on his face and a traditional Everybody Laughs Ending - accompanied by silly music.
The Star Trek: Voyager episode "Infinite Regress", where Seven of Nine starts manifesting the personalities of people she assimilated. So in the middle of her descent into madness we get a comedy scene where she's a Ferengi trader. And then we immediately switch to pathos as she becomes the confused mother of a Starfleet officer, who was supposed to meet him at Wolf 359 (site of the big battle in "Best of Both Worlds"). And then the Fridge Horror creeps in on a sweet early scene of her as a little girl playing with Naomi Wildman, when we're reminded that this little girl was assimilated.
Another one involving Seven of Nine manifesting other characters was when the Doctor's program is downloaded into her nanoprobes. Initially this is played for comedy, with Jeri Ryan doing a hilarous pastiche of the Doctor's pompous mannerisms. And then it suddenly turns dark when Seven learns what's happening, and she feels violated.
How I Met Your Mother had the episode "Bad News" which pretty much played out as a standard infertility story where Marshall and Lily go to a fertility specialist to get test to see why they are having problems conceiving (we already know Lily will get pregnant). The usual Hilarity Ensues with Marshall being locked in a bathroom having to get a sperm sample while his mother is talking to him through the door (unaware of what is going on). Robin has some bad first days at her new job where she becomes the new Butt Monkey. By the end everything seems to have worked out, Marshall and Lily are perfectly healthy, Robin has managed to turn things around at work and we think that the episode title is just a spoof. Then at the very last minute Marshall finds that his dad whom he was about to call with the good news, had a heart attack and died.. Marshall's reaction is a complete Tear Jerker.
The season 8 episode "Band or DJ?" has Ted feeling guilty that he's not really happy about Barney and Robin's engagement. Lily privately confronts him about this. Future Ted says, "By this point in my life, I'd been hurt quite a few times already." Cue a montage of clips we'd seen before of Ted getting hurt in funny ways: Young Ted as a camp counselor getting hit in the nuts by one of the kids, Ted getting attacked on a bad date, getting a tattoo (butterfly tramp stamp) removed and screaming in a high-pitched voice, getting beaten up by a female goat, a couple more nutshots, etc. and then Wham! Ted asking Robin if she loves him and getting rejected. Then a couple seconds later, all the clips are replayed faster with just the hits (and Ted's pained reactions) even funnier when chained together... Then Robin says, "No," again. And if that wasn't extreme enough, Lily's confession that sometimes she wishes she weren't a mother seconds later takes it Up to Eleven. Ted and Lily have a heart-warming moment. This is immediately followed by Marshall opening (the previously constipated) baby Marvin's diaper only to get covered in a massive spray of confetti.
Future Ted: Kids, it wasn't confetti.
"The Lighthouse" started out with Robin and Loretta trying to up one another and arguing who makes better scrambled eggs than Loretta but when Loretta unknowingly mentions grandchildren in front of Robin who can't have kids, the mood becomes a lot sadder.
Keeping Up Appearances has fun with this trope. Hyacinth shops for a second car; A crime thriller ensues. Hyacinth tries to help her sister fix her marriage; An epic foot chase ensues. Hyacinth goads Richard into repairing some electrics and babysits dogs; The dogs run away when the church is turned into a virtual war zone and explodes.
The final episode of The Good Life has Tom, Barbara, Jerry and Margo returning from a party celebrating Jerry's promotion - only to find that the Goods' house had been broken into, and needlessly and viciously vandalized when the burglars could find nothing of value to steal.
Tomica Hero Rescue Fire had an extreme example of this in one of the final episodes. Joukaen, an Axe Crazy fire-demon learns that humans are not the corrupt lifeform he thought them to be. Therefore he confronts his lord, Donkaen, only to learn that Donkaen turned him against the humans in the first place. So in a last effort to make up for this, he fights Donkaen and gets killed. One second after his death, the credits roll, with a very upbeat song as background music.
Used to chillingly good effect in the episode "Queen of Hearts" in Merlin. King Uther initially thinks it's hilarious that Arthur has been caught making out with Guinevere in the woods ("I was young once, I know about the temptations of serving girls!") only for him to coldly banish Gwen from Camelot on pain of death once Arthur declares his love for her less than thirty seconds later.
The episode also opens on a note of Mood Whiplash in which Guinevere's beautiful sunlit coronation is suddenly interrupted by Morgana waking up in a panic, the whole thing having been her prophetic nightmare.
Season four premiere has Arthur, Merlin and the knights wandering in a desolate village. Tension is mounting and they don't even know what kind of monster they are looking for. Suddenly, Gwaine takes a bite from an apple, startling everyone and breaking the tension. Only for Elyan to discover dead bodies.
The Wicked Day yanks its viewers around like crazy. Okay, it's Arthur's birthday. Good, Breather Episode. There's an assassin. Ok, Monster of the Week, can't be that bad. Uther gets stabbed and has only days to live.
The Doctor Oz Show tends to do this in episodes with serious topics. It may start off with somber conversations with women who have lost family members to cancer...and one tiny commercial break later, audience members are passing brightly colored balls representing poop through a plastic tube representing the colon, with everyone laughing and cheering at a successful "bowel movement" into a plastic bucket.
Game of Thrones features a lighthearted scene about Arya catching a pigeon and trying to trade it for a pie, then moments later witnessing her father's execution.
And this was just after she killed the pigeon with her bare hands, breaking the bird's neck.
In the same episode, a humorous scene in which Tyrion, Bronn, and Shae play a drinking game leads into the tragic story of Tyrion's first love, and how it turned out that she was actually a prostitute his brother had hired to make a man of him, and how as punishment for marrying her, Tyrion's father made him watch as she was gang-raped by his entire garrison.
In the third episode of third season, The Bear and The Maiden Fair, a funny rock song plays as the end credits song, right after Jaime's hand is cut off.
However, the crowning example of this trope occurred in Game Of Thrones S 3 E 9 The Rains Of Castamere during the wedding between Edmure Tully and Roslin Frey. Initially there were both hilarious moments (i.e. Walder Frey's utter Jerkassery and lecherousness on display) and utterly heartwarming moments (i.e. Talissa telling Robb she wanted to name their son after Ned Stark) with a light and happy atmosphere... then the eponymous "Rains of Castamere" song began to play as the Freys closed and bolted the doors, and Walder Frey loudly announces that he has a wedding gift for Talissa. Within ten minutes Robb, Talissa and Catelyn have been butchered along with almost all the Stark and Tully bannermen while their soldiers are slaughtered by the Bolton and Frey traitors outside, thus ending the Northern Rebellion.
Scream Queens acknowledges this very trope in its second series when John Homa is teaching the girls how to cry in scenes. One girl is told to laugh hysterically about stories she's telling at Christmas, when Homa suddenly tells her to imagine that the stories are about people who aren't alive anymore.
Done many, many times in Frasier, when a scene that is initially Played for Laughs becomes, upon further elaboration, much darker or more emotional than before. For example, Niles discovers that his wife Maris is cheating on him with his marriage counselor through a hilarious scene of Missed Him by That Much where both he and the counselor think they are preparing for a steamy night with Maris. This leads to an equally hilarious confrontation, and an even more hilarious scene where Niles' anger at his wife boils over while coaching a group therapy session; only for the scene to turn into a Tear Jerker halfway through when he bursts into tears and starts screaming at an absent Maris that he has never, ever cheated on her despite being tempted by Daphne, who treats him well and is a far better person than Maris is, for years, and finally breaking down sobbing that "I wanted to believe that [Maris has been always faithful to him] more than anything in the world, but now...now...I just can't see how I can...Now I just want to die."
Oh God, Daphne when Niles is having heart surgery. It's terrific writing and acting because the others make the jokes and act as you would expect but Daphne is sat wondering if she is going to lose Niles not that long after they have finally finally managed to get together. Almost as good is the terrific scene with Martin who is equal parts reproachful, compassionate and understanding with her when he says "It's hard as hell for all of us".
One particular part that stands out involves a candy machine. Frasier and Martin are arguing about the machine, in typical sitcom fashion. Daphne grabs a fire extinguisher, smashes the front of the machine, calmly hands Martin the particular candy bar he wanted, then completely breaks down.
In the episode before (S 10 E 7), we see Niles fretting about his toothache and the "1 in 10,000" chance that it could be heart trouble. Seems like typical Niles overanxiety, until the last scene where we find out he was right. Then it jumps back in the other direction when Niles is shown during the credits to be freaking out over being handed a water bottle.
NCIS does this in the episode "Two-Faced" (8.20). In many episodes, the final minutes after the climax are dedicated to comedy or romantic drama, and this is what it looks like when Tony and Ziva are sitting at a bar talking about their relationships (with a colleague and a liaison CIA agent respectively) when suddenly, the music changes and then... eyeball in the icecube. And their expressions: FUCK.
Kate's sudden death at the end of Season 2 too, actually done twice. She takes a bullet for Gibbs, but turns out to be wearing a bullet-proof vest. Everyone sighs in relief... and then she gets shot in the head.
The Six Million Dollar Man: Due to a decision not to air the tragic original The Bionic Woman two-parter at the end of the season (even though it was filmed as such), viewers saw Steve grieving for Jaime one week, and then his usually happy-go-lucky, womanizing self the next week.
Community has an episode where the guys are listening to a Video Will Pierce's mom left behind on a CD. The first track on Pierce's mother's CD is a recording of her pleading with him to understand the finality of death. The second track is hardcore gangsta rap.
The West Wing has one of these, completely unintentionally. Season 1 ends with someone opening fire on the president and crowd and as the visual fades you hear "Who's been hit? Who's been hit?" and then...there's the exceedingly peppy end credits music.
It's the same in any episode that ends on a serious note: the credits music is too damn happy! This is the fault of the DVD edition; during the original run, the end credits were almost always overdubbed with "Next on:" announcements.
The show often does intentional versions of this trope too. The most extreme is probably "Take This Sabbath Day," where the episode alternates between the gut-wrenching, extremely dark A-plot of Bartlet debating whether or not to commute the sentence of a man on death row scheduled to be executed by midnight, and the side-splittingly hilarious B-plot of an extremely hungover Josh experiencing Disaster Dominoes while bickering with a congressional campaign manager.
Done deliberately as part of the format in Doc Martin, every episode will contain one dark, serious and weighty storyline, and one light Quirky Town style story. They will then interleave throughout the episode, often with both story lines crossing through the same scene, and leaving the viewer pretty wrung out emotionally by the end.
Spencer: She used to say "Winder" instead of "Window".
Spencer: She's dead now.
Spencer: She fell out a winder!
Spencer: No, I'm kidding, she had a heart attack.
The third season Modern Family episode "Virgin Territory" goes from a serious discussion and realization of girls growing up quickly to scenes where Luke and Manny, both too young to drive, try to impress a girl by slowly driving Mitch's car.
Friends occasionally does this, and never more than in the episode "The One With the Morning After" which deals with the fall out of Ross sleeping with another woman behind Rachel's back after believing she's left him. Even though it's a fairly serious episode, the majority of it still has a few hilarious moments such as Ross and Rachel taking a brief break from their fight to order pizza and Rachel intentionally ordering anchovies mixed in with the toppings and sauce because she knows Ross hates them. However, the very last scene completely abandons the humorous aspect and goes completely serious. Even the brief moment where we see the remaining four other characters still trapped in Monica's back room is suddenly much more serious as they're all somberly listening in to the conversation, with Monica and Phoebe even breaking down into tears as they all realize that their two friends' relationship is over.
"The One With The Fertility Test" also has this. Most of the episode revolves around usual hi-jinks and Chandler freaking out about 'doing it in a cup'. Right at the end of the episode he and Monica discover they probably can't have children and the scene fades out with them sobbing in each other's arms. It's a punch in the gut that leaves you reeling and wondering what happened to so-called 'comedy'.
A lot of episodes with Monica and Chandler involve this, as the writers balance what is a genuinely sweet, heart-warming relationship and comedy. Their engagement episode goes from an amusing Zany Scheme to Chandler breaking down thinking she's left him and a gut-wrenching proposal, to the others coming in to crack some jokes, and then back to them dancing quietly together. Hell even their wedding vows switch between their tender declarations of love and Joey's messing up the order of service.
A Taxi episode had Jim buying an over-the-hill old racehorse and keeping it in his apartment. Typical Jim hijinks, but the horse inevitably dies. Jim gives it a funeral, and gives a truly sweet, moving eulogy that chokes up the rest of the cast (and plenty of viewers.)
Done rather tastelessly in an episode of America's Most Wanted. In the re-enactment, a desperate fugitive looking for shelter runs into an unlocked house to find two rednecks. They chase him out with baseball bats while banjo music plays and John Walsh wryly notes, "They weren't in the mood for company." Then the next unlocked house he goes to has an old lady who he brutally murders.
Kaizoku Sentai Gokaiger is rather prone to this, both within individual episodes and within the series on the whole. Episodes calling back to a specific series usually take on the tone of that series which makes for some rather odd juxtapositions with probably the most striking being the very light hearted and silly Carranger tribute episode being sandwiched between the character drama heavy Shinkenger double and the two-part, action packed introduction of Basco.
New Tricks jumps from light-hearted comedy to serious police procedural drama to seniors humour to Tear Jerker moments, often multiple times in the same episode. If an episode ends on a somber note, it can make the sudden appearance of the show's happy credits theme tune rather jarring.
The Adventures of Sherlock Holmes and Doctor Watson (a.k.a. Russian Holmes) contains a rare inverse example of Mood Whiplash, sad to hilarious. In "Hunt for the Tiger" (based on "The Empty House") Watson and Mrs Hudson enter Holmes' room, for the first time since his death, to the soft strains of a violin. Watson finds Holmes' violin, looks at it with a heartbroken expression and begins to play. Badly. After a few seconds the background music rockets to a crescendo and drowns him out.
The Aquabats! Super Show! episode "Showtime!" begins with the team trying to get their big break. When the team hears about something happening in the downtown area, they go check it out. On arrival, they witness a little girl fall into the clutches of aliens. The team and some other allies plan to stop them until SuperMagic PowerMan and Lanolin Lady show up, defeating the aliens and stealing the Aquabats' chance at fame. The episode maintains a light-hearted feel up to that point, when the little girl that was rescued uses SuperMagic PowerMan's headband to vaporize the superhero couple, and transforms into Space Monster M, who proceeds to terrorize a nearby city in his mecha form. Suddenly the plan no longer becomes to save the world to get fame, but because peoples' lives are at stake. It is here that the Aquabats, especially the MC Bat Commander who's been the occasional Idiot Hero, get their act together and outsmart Space Monster M, while the audience learns that the team is stuck in a "Groundhog Day" Loop.
At the end of the second-season premiere of 2 Broke Girls, where we finally met Caroline's imprisoned father Martin (always off-camera during the first season), Caroline, who up to then had been the doting Daddy's Girl, realizes that she has been a victim of his malfeasance too, and rather coldly cuts the visit short without saying anything to him.
Mash gave Col. Henry Blake a funny, moving, celebratory departure when he was finally released from his tour of duty as the 4077's commander... only to cut the legs out from under the audience and cast by having Radar walk in on the kidding-around-as-usual surgeons and announce that Blake's plane home was shot down with no survivors.
As a comedy set in war-torn Korea, Mash did this a lot. You could be laughing hysterically one minute and within seconds, you could be left like you've just been punched in the gut.
This was parodied in Futurama; one episode had a robot surgeon clearly based on Alan Alda's character, which had an actual switch that it would flip to jump between jovial goofing around and war-weary angst (labelled Irreverent and Maudlin respectively).
iHawk (despairingly): "This isn't a war...it's a murder."
(* flips switch* )
iHawk (Groucho Marx voice): "Dis isn't a war, it's a moider!"
Super Sentai can fall victim to this in how the mood of each series can differ; they can range from dark and serious (Jetman, Timeranger, Shinkenger, Go-Busters) to extreme camp (Carranger, Kakuranger, Go-Onger, Kyoryuger) and anywhere in between. At least some of these are market-based; when a dark sentai underperforms, the next one will be campy and vise-versa.
Call the Midwife seems to want to find out how many emotions it can make viewers feel in a single episode. Answer: All of them. Repeatedly, without ever once becoming melodrama. Probably the most notable, however, is the sudden jump from the horror of a bloody back-alley abortion to a cheerful summer fete in the space of seconds. In that particular case, the juxtaposition only underscores the horror of the first scene. Dammit, Heidi Thomas!
The season 4 Charmed episode "Hell Hath No Fury". Funny jokes about Paige messing with magic and getting an accidental Breast Expansion one minute, a serious story about Piper literally losing herself in rage and grief over Prue's death the next. One of the better-acted episodes in the series, oddly enough.
An episode of America's Got Talent featuring 6 year old Aaralyn and her 9 year old brother Issaiah. The entire intro plays them as an extremely cutesy brother-sister duo... and then they start singing their song, "Zombie Skin", a death metal ballad featuring Aaralyn screaming her lungs out. The looks on the judges' and audience's faces makes it clear they were NOT expecting that.
The '90s series American Gothic had a number of scenes with this, but one of the most outstanding is the episode "Learning to Crawl," which opens with an unusually cheerful scene of Caleb and Ben joking while Caleb helps clean the sheriff's office... then, in the middle of a line, 10-year-old Caleb gets nearly electrocuted in a sudden and random accident.
Talk shows, especially those of a comedy bent, often run into this when real-world events that aren't very funny take precedent. For example, Craig Ferguson has been acclaimed for his serious monologues following the deaths of his parents; the day the space shuttle Challenger exploded, Joan Rivers was hosting The Tonight Show and in lieu of a monologue came out and spoke about the disaster; in the weeks following 9/11, virtually every US talk show returned to the air with a solemn episode in which the host tried to make sense of not only the events of Sept. 11, but the purpose of shows such as theirs. Most recently, Conan O'Brien learned of the death of Robin Williams midway through the taping of his Conan series on TBS and announced Williams' death to a stunned audience.
Black Books: The first half of the final episode of the show is typical Deadpan Snarker alcoholism as the trio decide to head to a party. After they return the episode takes a turn when Bernard & Manny end up in an argument and Manny delivers a The Reason You Suck speech. Despite the rest of the episode still having comedic moments, it's still horrendously dark compared to the first half.
Tarrant on TV was an ITV series in which Chris Tarrant introduced clips from non-British TV. The clips were usually very funny — sometimes deliberately, sometimes not. Before the mid-point commercial break, however, he would introduce a very serious clip that was judged brilliant for its shocking drama, often a Public Information Film. In the context of everything else he introduced, they were, if anything, even more effective than in their own countries.