The Joker himself is a potent combination of Nightmare Fuel and premium Paranoia Fuel. If he's after you then he will get to you somehow, no matter how impossible it should be.
In most incarnations, the Joker is somewhere on the scale between comedic violence (Nicholson) and violent comedy (Romero and Hamill). What made Heath Ledger's Joker so scary is that Nolan removed the comedic aspect, but Ledger still played him as if he was doing everything because it amused him.
In fact, his performance even scared two actors during the scene where Joker crashes the party: Michael Caine and Maggie Gyllenhaal. Caine stated that he was so scared that he forgot his lines, and Maggie couldn't look at Ledger when the Joker was threatening Rachel with a knife.
The Joker's makeup. Not only is his permanent Glasgow Grin already terrifying enough, but the huge amount of eyeshadow he wears means that in many scenes (especially the interrogation scene) it looks like he doesn't even have eyes. The sight of those two black husks staring at the camera is enough to cause nightmares even before he does anything.
There's also the fact that, unlike many other iterations of the character, this Joker's skin is not all white. In many places, it's possible to see his natural skin tone contrasting with his white face makeup, giving us a stark reminder that at the end of the day, the Joker is just a human. While the white skin often distances the Joker from traditional humanity, here we're reminded that this guy is an ordinary person who manages to cause this much horror and chaos.
The Joker repeatedly claims through the film that he was not born a psycho, and states it only takes a day bad enough to turn a good man into something like him. It is never clarified if he is saying the truth or if he is just messing with people, as he makes fun of the whole concept of the Freudian Excuse. This leads to the inevitable question: Did something happen to the man who would become the Joker? And in that case, what was it?
When the Joker pulls a knife towards Gambol's mouth, he delivers a disturbing monologue:
''Do you wanna know how I got these scars? My father was a drinker...and a fiend. And one night, he goes off crazier than usual. Mommy gets the kitchen knife to defend herself. He doesn't like that. Not...one...bit. So, me watching, he takes the knife to her, laughing while he does it. He turns to me, and he says, "Why so serious?" He comes at me with the knife - "Why so serious?" He sticks the blade in my mouth - "Let's put a smile on that face!"
When the Joker finishes his story, he glances at one of Gambol's cronies and asks him "why so serious?" before brutally slashing and (presumably) murdering Gambol.
The infamous scene where the Joker demonstrates a magic trick to a group of men.
The Joker: How about a magic trick? [slams a pencil into the table, point first] I'm gonna make this pencil disappear...[Gambol's crony stands up and goes to attack him. In one swift motion, the Joker then slams the man's head onto the pencil, forcing the entire pencil—eraser first—through his eye socket; the crony collapses to the floor, dead, taking the pencil with him.]
The Joker: TA-DA! It's, ah, it's gone.
One of the most terrifying Joker-related scenes comes from when Batman interrogates him and the Joker reveals he's kidnapped Rachel in addition to Harvey, and they both have mere minutes to live. Batman goes berserk and starts trying to beat their location out of the Joker, up to bashing his head against a reinforced glass window so hard the window actually cracks. All Batman's severe beating does to Joker? It only makes him laugh HARDER! It only gets worse when you think about the Joker's line, "You have nothing, nothing to threaten me with. Nothing to do with all of your strength!"
A really horrifying scene is where the Joker tells Rachel the second scar story. Something about the whole scene reeks of sexual predation, and to make it even more horrible, there's the fact she knees him in the nuts, and he actually LIKES it!
One of the most Nightmare Fuel-filled moments was surprisingly one of the most low-key; when the Joker is videotaping/shooting his nightmare-porn of Brian the Batman Impersonator and orders Brian to "Look at me! LOOK!AT!ME!" That scene gets worse when Brian is done delivering the Joker's message and is of no more use to him. The camera cuts out just as Joker descends on the panicked hostage. The distorted sounds that are heard just before the tape ends, especially since we can't make out anythinghappening in the last bit of footage... When the newscaster says, "Sensitive viewers, be aware. The image is disturbing," he's not kidding.
Joker: Batman must take off his mask and turn himself in. Oh, and every day he doesn't, people will die. Starting tonight. I'm a man of my word. *laughs; drops the camera as Brian screams; footage abruptly cuts out*
And then you get to a moment later on in the film, when Joker burns his half of the money: one of Wayne's employees, Coleman Reese, has decided to go on to GCN and publicly reveal Batman's identity... only for Joker to call in and state he had a "change of heart" concerning Batman's identity.
There's also the discovery of Brian's corpse. Mayor Anthony Garcia was warning Harvey Dent that his arrest of 549 mobsters might put him in even more mortal danger. Right on cue, Brian's corpse suddenly bangs into the window Garcia is looking through, hung from a noose, wearing the Joker's makeup and facial scars. This scene is the nightmare fuel page picture for The Dark Knight Trilogy as a whole.
"Do you want to know why I use a knife? Guns are too quick, you can't savor all the.....little emotions. You see, in their last moments, people show you who they really are. So in a way, I knew your friends better than you ever did. Would you like to know which of them were cowards?"
Christopher Nolan originally thought of bringing us a more terrifying, twisted and psychopathic Joker. Here you can find the original designs for this Joker. However, Christopher Nolan felt that this joker did not fit his "Universe" so he decided change something to the Joker.
During the attempted assassination of the mayor/ Gordon's Disney Death; the guard who fires upon Garcia? That's the Joker. And he looksnothing like he does in the rest of the movie; even with the Glasgow Grin, you still can't really tell it's the same person.
The worst part about Two-Face was when he kidnapped Gordon's family, and Commissioner Gordon, whom many tropers strongly identify as a father figure, cried and begged helplessly for their lives. The thought of a father (whose job is being a policeman, no less) being unable to protect his children is just pure Nightmare Fuel, let alone Adult Fear at it's finest. The music in that scene, appropriately titled "Watch the World Burn", just makes the whole thing so much more intense. It starts off quiet, but gradually becomes louder to the point where it's unbearably intense. There's just something in there that truly and absolutely defines Harvey's Sanity Slippage.
Two-Face: Tell your boy it's going to be alright, Gordon. Lie, like I lied.
Alfred's speech on being in Burma, just because of how true it felt.
Alfred: A long time ago, I was in Burma, my friends and I were working for the local government. They were trying to buy the loyalty of tribal leaders by bribing them with precious stones. But their caravans were being raided in a forest north of Rangoon by a bandit. So we went looking for the stones. But in six months, we never found anyone who traded with him. One day I saw a child playing with a ruby the size of a tangerine. The bandit had been throwing them away.
Bruce: Then why steal them?
Alfred: Because he thought it was good sport. Because some men aren't looking for anything logical, like money. They can't be bought, bullied, reasoned or negotiated with. Some men just want to watch the world burn.
When Alfred later finishes the story with how they caught the bandit, he flatly states, "We burned the forest down." In order to get the bandit, Alfred was forced to give the bandit exactly what he wanted and in the process become a man as cold and unrelenting as the bandit himself; a man who would burn everything around him to get at his objective.
A fat lunatic complains of stomach pains and rants that the Joker told him that a light would come from his stomach in this high, childish tone. It comes out of his stomach all right...in the form of a bomb the Joker implanted inside of him.
The Joker aims to destroy Gotham City from the inside out, and part of his "plan" involves corrupting the city's heroes — Batman and Harvey Dent — by making their lives hell until they snap. Thankfully, he doesn't succeed with Batman. Harvey Dent, however...
Almost the entirety of Joker's theme. One particular part can shock a few. Once the theme gets quiet, it then builds up a note, a musical Hope Spot as if it's going to transition into Batman's theme with a higher note...boom. You're suddenly hit with a deepScare Chord, a low booming note that drags on for what feels like minutes. It almost feels as if Joker, on top of everything he had done in the film, is even actually controlling the music, just to screw with the viewer themselves!
As scary as Ledger's Joker and Two Face are in the film, the early concept art is really something else... The first iterations of Two-face were more realistic, with less extensive damage; test audiences actually found the more subdued, realistic damage to be so unsettling, to the point of unintentional Nausea Fuel, that the Two-Face we currently see was used instead. The Joker pales in comparison to Two-Face's scar-ified half of his face. Whatis keeping hisEYEBALLin theSOCKET!?
Though Scarecrow only shows up in one scene, he's still making his horrifying fear toxin, and now evidently contaminating recreational drugs with it. When the Chechen brings a victim of the toxin to Scarecrow to show him, the poor victim can be heard screaming, "Please! They're crawling in my mouth! Get them off!"
Scarecrow:Buyer beware. I told you my compound would take you places. I never said they'd be places you wanted to go.
Harvey Dent interrogating Thomas Schiff. Not only is Schiff's unhinged giggling and bug-eyed stare off-putting, but Harvey brings some serious lashings of nightmare fuel on his own. He conducts the interrogation in a back alley rather than at the police station, demonstrates that the gun he brought is not a toy before pointing it at the man's head, then states that he'll decide Schiff's fate by the toss of a coin. This is the most respected man in Gotham.
This one zig-zags a little; when Dent flips the coin, he tells Schiff that he'll shoot him if the coin comes up tails. It's revealed later on that it's a double-sided coin, both heads. Meaning Dent had no intention of shooting Schiff. However, the fact that he would use such intimidation tactics on a mentally ill person doesn't really paint Dent in the most morally upstanding light, and this is before he becomes Two-Face. Even Batman calls him out on it.
Batman: You'd leave a man's life to chance?
Agent Of Chaos, the music that plays when the Joker is being interrogated only to escape and Batman is trying to save Rachel, while at the very end it slips into Tearjerker territory to parallel her death, the vast majority is very intense, chaotic and adrenaline filled, hinting at a great and terrible danger. It truly feels like it could be a second Leitmotif for the Joker himself.