Ricardio not only threatening to cut out Princess Bubblegum's heart out, then showing a horribly grotesque detailed◊ close-up of his face and having him say "And make out with it" with creepy opera music playing in the background.
The scenes of the Ice King with no heart. Sure- he's a jerk and he starts off as a harmless villain in the series, but he didn't deserve to be treated so horribly by Ricardio. He's too much of a woobie. The fact that the Ice King explicitly stated that Ricardio threw him in a dumpster and left him for dead really shows us just how evil Ricardio actually is.
One of the worst parts had to be the fact that was that Ricardio was going cut out Princess Bubblegum's heart using broken glass bottles.
"When Wedding Bells Thaw" was the only episode where the Ice King is not only evil, but downright diabolical. He doesn't just kidnap a princess, stick her in a cage, and marry her against her will. He actually BRAIN-WASHES a princess and forces her into WANTING to marry him! That poor old lady princess... She was so terrified she was actually crying. And the way she was so angrily protesting as the Ice King lowered her down. . . We all know that the Ice King isn't a bad guy- he's a Jerkass Woobie, but this moment very well could have been his moral event horizon, if he had continued in this direction.
"Freak City". MagicMan. You know an animated series is gold when you, a grown-ass adult, have nightmares about its Q analogue.
One of the first things he does is magically turn a bird inside out. The worst part about the inside-out bird is that it doesn't die. It flops around on the ground for a little bit and struggles to get away- a true Fate Worse than Death if there ever were one.
Jake: Think happy thoughts - little cute bees, little babies, tiny tiny bunnies
"Dungeon" had PLENTY.
Finn's "guardian angel" is horrific, mainly because the sudden change from cute to scary can catch you off guard. She also says something along the lines of "I'm going to boil you alive and eat your flesh" before showing off her... disgusting face?
Demon cat thing! Sure, his knowledge of "almost everything" was rather great, but something about his voice and composure...
Cat: I am going to unzip your skin and wear it like a little coat.
The angry face Princess Bubblegum made at the end.
Princess Bubblegum is scary, depending on who you talk to. For such a cute character, she has her very terrifying, unsettling moments. For some people, she's the scariest character in the show BECAUSE she isn't expected to be, based on her cute appearance and affable demeanor. Her creepy scenes come out of nowhere, and are always unexpected.
Season 2
Pen Ward warned that "It Came From the Nightosphere", would be filled with this. And rightfully so!
Marceline's Dad. A soul-sucking malevolent Eldritch Abomination who shows his innards to other people for fun. His voice is creepy. He sounds like a pretty average, nice man. Definitely not the voice you'd expect from such a character. Also when he turns to the Ice King and although we can't see it that well, his face basically EXPLODES.
Perhaps it's the more subtle things that make Marceline's Dad creepy- like the way he walks. His gate is like a mix of a creeping spider and an Uncanny Valley marionette.
Marceline looked pretty scary whenever she had red eyes and sharp claws.
In "The Eyes," you can see a tiny, skeletal figure next to Finn and Jake's window, hanging itself.
The Royal Tart Toter. He's insane, uncanny valley, has deranged eyes, foaming at the mouth and everything. The Candy Kingdom doesn't seem to deal with their mentally ill very well, seeing as how the Tart Toter and Lemongrab just sort of wander around, mentally unstable, with nobody helping them.
The torture the gnomes put Finn through in "Power Animal".
The very last line of that episode.
Jake:Let's go eat Cinnamon Bun.
Much of "Susan Strong". Susan going completely manic, and her gathering up her hyoomans to eat everyone in the Candy Kingdom, (except for red stripe man.)
Jake's scary line: "We could rule them like gods! *squints eyes, rubs hands, talks in low, soft voice* Angry gods..." Of course, Jake was kidding, but the way he said that line was insanely creepy.
The fact that he knows how to enter the realm of the dead and is good friends with Death himself is more than a little disturbing.
Plus the quick scene in the season finale where he brings tea to a Lich-possessed Princess Bubblegum and upon catching sight of her sprouts fangs and hisses like a cat before running away on all fours. What the hell is that guy?
The season 2 finale as a whole. The Lich, who looks as terrifying as expected? Check. Princess Bubblegum hospitalized in serious condition? Check. Her SKIN MELTING OFF HER BODY AS FLAMES DANCE ABOUT HER? Check.
Unlike most villains on the show, The Lich is a Complete Monster that even Finn and Jake had trouble dealing with.
If you look closely you can see very tiny and faintly seen pupils in the Lich's eye sockets, for some reason it's just disturbing.
Here's the link. The low voice for Bubblegum actually makes it worse.
During the first showdown with The Lich, Finn shoves his sweater into the Lich's eyes, pulling his skull out and shattering it to pieces. How does the Lich react during all this? He laughs.
And at the very end of part two, it's shown that the snail is still possessed by the Lich's evil influence... Probably for the sake of cliffhanger, but still...
What makes this even worse is that any further appearance of the snail shows that the Lich is silently watching Finn and Jake's every move.....
Hell, the Lich was redrawn as the creators didn't think he was scary enough.
Season 3
The revelation that those gladiator ghosts in "Morituri Te Salutamus" were originally best friends, just like Finn and Jake, who were driven insane and forced to kill each other.
Before that, how the gladiator ghosts would be in visible despair as they fought, either for killing their freind ("Forgive me, Valius!") or for their friend betraying them ("Et tu, Walius?").
Also when Finn become insane and tried to KILL JAKE. Granted, he was faking it BUT WE DON'T KNOW THAT!
At the end of this episode when the gladiator ghosts are floating up to the heavens with the creepy sounds in the background gave me uber-chills for some reason...
According to Andy Ristaino, the gladiator ghosts were LOVERS. Presumably, they lived together, slept together, and loved each other dearly... and they killed each other. The revelation that they were romantic partners in ADDITION to being friends just adds on even more nightmare fuel, and it's an even bigger tear jerker.
"Too Young" - Princess Bubblegum's flashback of creating Lemongrab. Hilarious to some people, but it can be very unsettling to others to watch somebody panic by the sheer horror of being alive...it's especially scary because the scene is both terrifying from Princess Bubblegum's perspective, and Lemongrab's. The creepy music in the background, and the gloomy atmosphere of the lab, doesn't help much. Also the ending of that scene where LEMONGRAB'S EYES ROLL BACK INTO HIS HEAD, ONLY LEAVING THE WHITES EXPOSED AS HE SCREAMS!
There was a very creepy scene storyboarded for "Too Young" that didn't make it into the episode, most likely to save time. Normally, Lemongrab is just an obnoxious, unhinged jerk, but in THIS scene, he's downright terrifying, and doesn't show qualms about terrorizing small children and making them cry. In the scene, Lemongrab says, "Anyone who disagrees or disobeys will be thrown into the dungeon." A little candy CHILD gasps, and asks, "The Royal dungeon?" Lemongrab turns to the kid angrily, and shouts, "Thirty-TWO days in the dungeon for you!" The kid stutters a bit, trying to defend himself... until Lemongrab makes a horribly creepy, deranged Nightmare Face and shouts "DUNGEON!" The kid leaves the room in tears.
Lemongrab's laugh. Basically, a totally joyless, insane laugh as his head flails around with weird squishy noises. Even everyone else is creeped out.
This is more of Fridge Horror or blink-and-you'll-miss-it, but it's incredibly unsettling. Everybody in the Candy Kingdom was imprisoned, and set to stay in the dungeon for several years. Lemongrab doesn't seem to understand anything about people's most basic feelings or needs. There's a great possibility that if he had stayed ruler of the kingdom, everybody would have spent their entire lives in the dungeon. This is even worse for the candy people who were stuck in the very tiny cages suspended from the ceiling. Imagine being stuck in there for an extended period of time.
Lemongrab himself creeped out a significant portion of Adventure Time fans- thanks to his psychologically unstable personality, banshee-like screams, and his Uncanny ValleyDull Eyes of Unhappiness.
Fionna and Cake. It was a pretty light-hearted episode, but one scene is downright terrifying for adults, especially women, to watch. Prince Gumball says, "Fionna, I have to show you something." He takes Fionna's hand and leads her up to his bedroom. "Hey, is this your bedroom?" Fionna asks. We see Gumball's bed, covered in rose petals, illuminated by an off-screen spotlight. We see Gumball step towards Fionna with a serious expression on his face, as he unbuttons his shirt. "Woah... heh heh..." Fionna says nervously. Up until The Reveal, where the audience sees the REAL Prince Gumball frozen to the ceiling, it looks like Gumball's about to RAPE Fionna!
Horrifying from Cake's perspective. We see Cake standing in the hallway, listening to what's happening upstairs. We hear a loud thumping, and Fionna crying, "Get off of me!" Cake's terrified reaction sells it. And when she comes back to the room, she sees Fionna's dress completely tattered. She launches herself at Gumball and attacks him, screaming "Don't you touch her!"
"The Creeps," as the first Halloween episode, had its moments. The worst part was probably Cinnamon Bun's splattered remains inside a closet!
Or the green, slimy ghost that came out of nowhere! Made all the scarier with the Real After All revelation and the sudden flashback that occurs right before Finn makes himself forget about it.
Even though it was just a wax replica, PB melting was creepy.
Lub glubs. The name not sound scary at first, but when you find out what they really are.... They look like nothing more than harmless inflatable pool toys, but then we find out that they are actually formless Eldritch Abominations that are covered in teeth. Also its strongly implied that they killed off the last remaining humans.
The episode "No One Can Hear You" is full of this.
Finn waking up in the hospital and finding the Candy Kingdom absolutely empty. This is a show with Loads and Loads of Characters, so having Finn and Jake be the only ones there for most of the episode is downright terrifying.
Also the fact that the citizens of the Candy Kingdom were trapped constantly licked by the Deer (which one would assume to be seriously painful to a candy person). The only two people that could help them were Finn, who was in a coma with both of his legs broken, and Jake, driven insane due to a head injury and believing that everyone else was just hiding. Now imagine the poor citizens of the Candy Kingdom constantly moaning in anguish for help that would never come. Suddenly the title for the episode becomes all the more fitting.
"New Frontier". The episode involved Jake having a dream revealing the details of his own death, called a "croak dream," and then trying to make sure the death happens once details from the dream start to appear in real life. He claims he's doing so because You Can't Fight Fate, but as the episode goes on, he starts to come across as downright suicidal. Finn gets a bit suicidal as well. When they're in the lake, Finn refuses to leave Jake's side even though he's drowning, saying he'll stay by his side "forever". That leads to some scary implications. If Jake died, would Finn...choose to follow?
When Jake's dream was nearly over, out of nowhere the Cosmic Owl appears and lets out a high-pitched shriek, accompanied by a sudden noise.
A great overlap between this and Tear Jerker is found in "Holly Jolly Secrets," when we learn that the Ice King used to be a man named Simon Petrikov, who was engaged and becoming an archaeologist. He was sold what would become his Memetic Outfit crown, and put it on his head just as a joke for his fiancé Betty. This small contact with the magical artifact led to a slow descent into madness, quickly making way for a Noodle Incident that caused Betty to leave him. The crown then continued turning him into a monster... turning him into what he is now.
Simon: I don't know when it'll end.... (almost whispering) I'm really scared...
Especially considering he literally refers to Betty as "My Princess" and begs her to come back - and it gets worse when you realizehe was most likely responsible for her death.
The subtle take on a Scare Chord that was used when we first see Simon open the cabinet and show his audience the crown.
For some reason, this troper was insanely creeped out about Simon's voice gradually, and subtly changing, into the Ice King's. The physical transformation was clear, but the vocal change really helped to emphasize how his body AND mind were changing.
The implication that either the crown either protected the Ice King from one of the events that started the Mushroom War, or made him do so through his power over ice and frost.
The worst part is that Ice King's in denial about once being human. It appears Ice King is too far gone to ever be human again.
"Please love me again, Betty!"
His entire monologue was one minute and a half of pure, concentrated, psychological nightmare fuel.
Hello. My name is Simon Petrikov. I'm recording this tape so that people will know my story. I was studying to be an antiquarian of ancient artifacts. Now, I've never believed in supernatural stuff myself, just had a fascination with superstitions. But everything changed when I came into contact with this item. After purchasing this crown from an old dock worker in Northern Scandinavia, I brought it home and excitedly showed my fiance, Betty. I jokingly put it on my head just for a laugh or something. And that's when it started... the visions. I fought with them, shouted at them until I realized it wasn't real! It was the crown! I quickly took it off, and saw my fiancee in front of me, looking at me with such contempt! What had I said? What had I done when I wore this crown? All I know is, I never saw Betty again. Since then, I now see the visions always whether or not I wear the crown. They tell me the secrets... the secrets of the ice and snow... that the power of the crown will save me with its frost. I don't know yet what this means. As you can see my skin is beginning to turn blue. My body temperature is lowering in a supernatural rate, to what is now about 30 degrees Celsius. I don't know when it will end. I'm really scared. I know my mind is changing... but I've already gone too far to know what to do. I want people to know that... if I do things that... if I do things that hurt anyone, please, please forgive me! Just... watch over me until I can find my way out of this labyrinth in my brain and regain my sanity! And then maybe Betty, my princess... maybe you will love me again... Please love me again, Betty!
This is made even more terrifying with the implication that the Ice King is so obsessed with princesses because he's trying to get back his 'princess' Betty.
All those dead animals lying around in Wildberry Princess's castle with their lifeless open eyes...
Finn's unabashed conquest to have it his way. He mortally injures multiple forest creatures in the process, completely going against his code to help anyone. Eventually he sees the errors of his ways and heals them all..
In "Ghost Princess", Clarence's death. Lets just say that Jake had a very good reason to swear off cheese spread...
"Dad's Dungeon" had 2 particular scenes. The first being the fruit witches when they went bad and second being the monster at the end.
Especially the Fruit Witches sequence. Finn in Jake are in a surreal room full of fruit while beautiful women are floating around telling them to take a bite. Jake is Genre Savvy enough to know it's a trap so he stuffs an apple into one of the women's mouths. Vines protrude out of her mouth and eyes and cover her whole body. The vines then fall apart, leaving behind a huge apple. The other women turn into demons and ferociously tear apart the apple, and feed the shreds to what looks like miniature lub glubs in their hair, revealing what appears to be BONES. ON A BLOODY APPLE CORE.
After the demonic girls are done feeding they leave behind an apple core with a dark suspicouly meaty looking center with bones coming out of it and some visible blood. The girls then chase after Finn and Jake, after seeing what happened to the apple, just imagine what would have happened to our heroes. This one really takes Family Unfriendly Death to an extreme.
And regarding the monster... Imagine a lubglub, but 20 times as big with tentacles and a diamond eye, and it justkeeps laughing...
Season 4
"Five Short Graybles". PB and Pepbut actually killed a cute little jellyfish for the sake of making the greatest sandwich ever by cooking it. If you think about it, it died in a pretty awful way.
The ending of "Web Weirdos", where Finn and Jake are buried under a mountain of baby spiders infinitely gushing out of their mother's backside.During the fade to black.
Jake: Love like theirs will always find a way. It'll crawl all up over you and drain your body fluids, poisoning you slowly until you pass out. Finn:WAAAAAHHHHH!!! Jake: Circle of life, Finn. Circle of life...
Jake in "Return to the Nightosphere". He turned into some kind of gross demon for real: http://youtu.be/vwlO3o3vmRo.
Nightosphere monsters. One of them looks like it had one side cut off.
As they pan across the horizon to show us what the Nightosphere really looks like, the only sound effect that can be heard leaves him shaking in fear. It's a sound effect that sounds like an old woman dying a horrible, slow, painful death.
And Marceline's Chaotic Evil form complete with creepy, modified voice.
NO ONE LEAVES THE NIGHTOSPHERE.
You thought demons were creepy with the Nightosphere Amulet? Here's Finn under its control◊.
The cruel and bizarre punishments. One demon was forced to eternally vomit bananas (and bananas are considered to literally be shit in the Nightosphere,) and one had his entire head turned into abdominal muscles. According to Andy Ristaino, they didn't get better, and their situation is probably far worse right now.
At the end of "In His Footsteps", the Lich has returned and appears to be plotting something along the lines of vengeance.
Not so much High Octane Nightmare Fuel as it is High Octane TRIGGER Fuel. When Finn and Jake are having a nasty argument (lots of shouting), BMO, who just got home from soccer, sits on the floor quietly, absent-mindedly rolling his soccer ball back and forth. This brings to mind the way a child reacts to his dysfunctional parent's arguing. The scene is pretty weird and mundane to the average person, but it probably caused countless fans, who grew up in dysfunctional households, to cringe or just feel disturbed.
The whole premise behind "Princess Monster Wife," which is essentially about Ice Kingstealing the princesses's body parts. We see LSP cut open, PB with no head, and (disturbingly) Turtle Princess with about three fourths of her head GONE.
The way PB tries to talk with most of her head missing. Incomprehensible gurgling. Anyone who has seen the episode of South Park "Britney's New Look" will shudder at this episode. Sweet dreams...
And of course the titular "Princess Monster Wife" in question...'she' is about as disturbing as you can imagine...
YMMV. This troper thought she was beautiful.
The way the Princess sounds- three voices at once. Also a HUUUGE Tear Jerker- as when she cries, we hear three voices crying.
Don't forget the fact that the combined Princess is alive...and essentially takes herself apart, which could be seen as killing herself for the good of the other Princesses.