Spider-Man/Nightmare Fuel

Monster Ock. There's no way to defeat him: all you can do is run, and pray he won't catch you. Look up videos of him on youtube, and many of the comments will be similar to: "This scared me to death as a kid!"
- "DIE!"
- Similar to Monster Ock, there is Spider-Carnage. Imagine your favorite childhood character, turned into a horrible monstrosity that wants to kill everyone. *Shudders*
Marvel's Spider-Man Noir is an Elseworlds-esque comic retelling Peter Parker's story in a film noir setting. It's also chock full of disturbing stuff, including a scene of Fancy Dan being covered and consumed by a swarm of palm-sized spiders, Peter's nightmare sequence after being bit by one of the same spiders, a mutant, circus freak version of The Vulture with some interesting dietary quirks that we get to see him indulge in including tearing Ben Parker apart with his hands and teeth, the reveal that this world's version of Norman Osborn is called the Goblin because of his horribly deformed face, which he hides behind masks and makeup, Kraven the Hunter becoming a living host for the giant spiders, the list goes on. The sequel is even more nightmarish, with the subtitle "Eyes Without a Face", the Sandman being an inhumanly strong thug who pops heads like bubble wrap and Dr. Otto Octavius conducting strange, forbidden experiments on "the lower races" to make them the perfect slaves. The ultimate fate of Robbie Robertson is that he's almost completely dead to the world and only responds to direct commands involving physical actions. He has a large indented scar on his forehead from the brain surgery performed on him.
- Speaking of Spider-Man, the Tordenkakerlakk from the graphic novel Hooky is worth mention, due to the myriad of grotesque forms it takes throughout the book, for the sole purpose of stalking a little girl who has been alone for 200 years.
  - The Amazing Spider-Man story arc "Shed" is this. There's no return to Curt Connors for the Lizard. Not now. Not after what he does.
Two books published by Marvel about the villain Carnage, Mind Bomb and It's A Wonderful Life. The character of Carnage is already up there to begin with, having been in prison serving ELEVEN consecutive life sentenced for murder before obtaining the symbiote, and after obtaining it, his only goals were to kill as many people as possible. The entire plot of Maximum Carnage was that Carnage wanted to kill everyone in Manhattan. He's a killer with no style or gimmick, who only wants to kill, preferably by brutal, gory means. But these books... both involve Carnage using the symbiote to connect to the minds of other people, which allows us to see what's in Carnage's mind. He lives in a world of corpses, willing victims, ark humor and frightening landscapes all of which house his knowledge, desires and memories of the past. There is even a special area where Carnage spends time hacking up Spider-Man copies for fun. One panel of Mind Bomb shows the "real world" as he calls it, which features a man eating intestines and holding a cup labeled "urine sample" as a drink glass, an elderly woman in bondage gear and a cop with a KKK hood shooting a man. In Mind Bomb, the man he's connected to, Dr. Matthew Kurtz, goes completely insane from this experience. The second book plays more to Cletus Kasady's history as Dr. Kafka and John Jameson are connected this time, each mutating into a vicious creature (John turned back into the Man-Wolf, a previous villain form, and Dr. Kafka slowly changed into a cockroach) finally ending when a young black kid named Billy shows up deep within the area of repressed memories. Carnage threatens to kill him if they get too close but seems unable to (it's hinted that Billy was a childhood friend, but the details beyond this are never really said) and finally has a breakdown, releasing the two but left in a catatonic state. The artwork is graphic even for a Carnage story and the cover of Mind Bomb has him perched on a pile of human skulls. The oddest part? Both books were approved by the CCA.
- Even worse, IAWL seems to play with the idea that the people running the mental hospitals that house supervillains may actually be more evil than Carnage. Mind Bomb showed him as oddly intelligent for a supposedly uneducated guy but IAWL opens with Carnage ranting about the change in management. He even seems to be more than aware that many "accidents" that are resulting in patient deaths during their transfers are intentional and even calls out that the car crash that killed Wolverina (not Wolverine) was on purpose. This alone might be the most frightening aspect, Carnage himself calling out someone else for being worse than him and being right.
During The Gauntlet, the Lizard kills his son. Not because he transformed with him close by; he hunted him down to prove he was The Lizard, and that Connors was dead.
Venom himself was often this to Spidey, because of all the information he had about him, not to mention all the creepy commentary he would make and that constant big-toothed grin. Granted, he soon became more of an anti-hero, but he often went overboard when dealing out punishment to wrongdoers, which didn't exactly make him less scary.
Kraven's Last Hunt. Kraven the Hunter literally buries Peter alive and assumes the Spidey identity, only going extra rough on criminals while Peter's friends and family have no idea where he is for days. The What If? issue was even worse, with Peter actually having died and being eaten alive. Oh and every superhero is faced with persecution worse than usual, and we have no idea what happens to them (the narration says MJ's crusade on Superhuman rights makes her famous-it doesn't say she actually accomplished anything).

Movies

In the first movie, the appearance of the Green Goblin.
Norman hallucinating that the Green Goblin is laughing and talking to him.
Green Goblin presenting Spider-Man with a Sadistic Choice.
- Following that, there's the Goblin's beatdown on Spidey.
Peter is worried about Mary Jane and calls her house to make sure she's okay, but instead of Mary Jane, he gets the Green Goblin on the other line, who giggles and says in a creepy sing-song voice, "Can Spider-Man come out to play?"
After being forced off of Peter, the symbiote latches on to its next host with a vengeance. Seemingly in order to ensure that it won't be rejected again, it goes all the way with Eddie Brock, literally pouring itself down his throat. But by far the creepiest part of that scene was when Brock started to enjoy it.
- When the symbiote forcefully bonded with Peter.
Doc Ock killing the doctors in the second movie. Don't believe me? See for yourself.
- The scariest part? Otto was unconscious. His tentacles did that all on their own. Imagine waking up after a horrible accident, only to find yourself in a hospital with everyone in the room dead. You begin to hear a voice. Four, in fact, each one of them telling you to do horrible things.
In the third movie, the symbiote attaching itself to Peter as he lay asleep.
The depiction of Norman's and Harry's Sanity Slippage.
The accident that made Norman insane.