Lightmare Fuel

Lightmare Fuel is when Nightmare Fuel is Played for Laughs. It is the perfect combination of the truly scary with the truly funny. This often happens in comedy works, typically Black Comedy, but can just as often occur in horror stories.

A Sub-Trope of Mood Whiplash. Compare Faux Horrific and Bloody Hilarious.

Anime and Manga

 * Kurosagi Corpse Delivery Service. Most of the series features a lot of this trope. In the first book, one of their stories features a corpse  who gets vengeance on her killer by telling him a joke. It drives him insane.

Film

 * Ghostbusters. The Librarian scene. In the DVD commentary, Ramis and Landis stated that they achieved the perfect balance in that moment of people in the audience during the first screening of both laughing and screaming at the same time.
 * Pee Wee's Big Adventure: The encounter with Large Marge.
 * Twilight Zone the Movie. "You wanna see something really scary?"
 * An American Werewolf in London is seemingly made of this in some parts. Griffin Dunne and David Naughton are laughing it up, joking about the superstitious villagers as they walk along the moonlit road one second, and in the next second Dunne's throat is ripped out on-camera and Naughton is slowly bleeding out from a werewolf bite.
 * "MacGoogles the Scottish Frog" in Max Keeble's Big Move. He is genuinely creepy-looking... and yet you won't be able to stop laughing.
 * In the "musical comedy" version of Little Shop of Horrors, we go from laughing to cringing, especially once Seymour starts feeding Audrey II whole human beings.
 * Shaun of the Dead: Once they finally get refuge in the local pub, they are quickly besieged by zombies. As Shaun and the others try to keep the zombies at bay with a rifle, Shaun's mother admits to Liz (Shaun's ex, although his mother isn't aware of the breakup) that she was bitten by a zombie earlier in the movie, dooming her to death and resurrection. She dies in Shaun's arms as he begs her not to leave him. This is followed by a genuinely tense Mexican standoff over what to do with Shaun's mother - David reckons they have to shoot her, Shaun and Ed are hysterically protective - which is punctuated with some of the movie's funniest dialogue.
 * In Jaws, the scene where Brody is complaining about having to dump chum (chopped up fish and fish blood) into the ocean begins with the line "Slow ahead. I can go slow ahead. Come on down here and chum some of this shit." and ends with the line "We're gonna need a bigger boat", having gone from funny to scary in a nanosecond when the shark abruptly appears.
 * In Sleuth, the story jumps from funny to horrifying within a second. Some scenes you might alternate between smiling and being afraid for the characters' lives several times within one moment. You could even find yourself grinning while thinking "I think something horrible is going to happen any minute".
 * The 1989 comedy The Burbs on the surface seems to be a wacky "mistaken identity" comedy about three childish protagonists who suspect that their next-door neighbors are a family of serial killers. The protagonists' wives, of course, think they're just being stupid. Wacky hijinks fill the rest of the movie, until the protagonists discover that the the trunk of the next-door neighbors' car is filled with decomposed human remains. Because the neighbors really are a family of serial killers.
 * There are more than a few moments of this in Beetlejuice.
 * Gremlins. The little monsters are hilarious... until they start killing people in messy, messy ways.
 * Zombieland. The explanation of Rules #1 ("Cardio") and #2 ("Double Tap") are accompanied by a visual of people being graphically attacked and killed by zombies. They are hilarious and tragic and scary all at the same time.
 * The various "zombie kills" (especially the "Zombie Kill of the Week").
 * Abbott and Costello Meet Frankenstein, especially the scene involving the Absurdly Ineffective Barricade.

Live Action TV

 * Being Human constantly whips between wacky sitcom hijinks and extremely gory supernatural horror, which can be more than a little jarring.
 * American Horror Story has a moment of this. In one episode, Hayden, Ben's former mistress and student, discovers where he lives and threatens to reveal to Ben's pregnant wife that she is pregnant with her and Ben's love child from the affair. When Ben agrees to go someplace with her to discuss the pregnancy, Harvey comes out of the blue and hits her dead in the face with a shovel. Upon realizing that she's not dead, he hits her again.

Web Original
"Input: 1 lb. raw ground beef
 * Quite a few articles from the SCP Foundation are simultaneously somewhat scary and hilarious.
 * SCP-426: I am a toaster that can only be spoken of in the first person. My entire article is consequently written in this manner, which leads to a great deal of amusement. However, prolonged exposure to me also has some... unpleasant side-effects, leading two of my previous owners to, respectively, plug themselves into an electrical socket and eat so much bread their stomach exploded.
 * SCP-914's experiment log, in between straight-up funny.

Setting: Very Fine

Output: [DATA EXPUNGED]. Appeared to be [DATA EXPUNGED] ██████████ started mooing ██████████ bitten subject [DATA EXPUNGED] ██████████ escaped into ██████████ screaming ██████████ [DATA EXPUNGED] hungry for [DATA EXPUNGED]. Subject immediately terminated."


 * Similarly, 447. It's perfectly safe as long as it doesn't come into contact with dead bodies. It's a good lubricant, salad dressing and improves gasoline efficiency as long as doesn't come into contact with dead bodies. It seems to be entirely benevolent but must never come into contact with dead bodies.

Western Animation

 * Courage the Cowardly Dog is pretty much made of this, being a genuinely creepy cartoon that happens to be a comedy.
 * Similarly, The Marvelous Misadventures of Flapjack is prone to bouts of some seriously scary imagery that's played entirely for laughs.
 * Adventure Time often falls into this. Given that Pendelton Ward works on Flapjack, it was probably inevitable.
 * The Ren and Stimpy Show was all about this, at least up until John K. was kicked out from it. The episodes produced by Games Animations, much degraded in quality, also stepped in the territory of Nightmare Fuel frequently - however, with these, it was unintentional and more prone to be genuinely horrifying rather than just used for comedic effect.
 * SpongeBob SquarePants does this a lot, especially after The Movie.
 * The Simpsons' "Treehouse of Horror" episodes basically run on this trope.
 * My Little Pony Friendship Is Magic is known to use this trope occasionally. If the show's Nightmare Fuel page is anything to go by, it might be overshooting.
 * Peri stalking Entree in the Spliced episode "Stuck Together" is portrayed as this.