- Dr. Connors visibly mutating into The Lizard in the first episode.
- The Neogenic Nightmare arc seems to have been written with the express purpose of traumatizing children. Let's see what it featured:
- Michael Morbius becoming a genuinely creepy vampire. As if that isn't bad enough, instead of sucking blood using his fangs like most vampires, he drains plasma through small suckers in his palms instead (oddly enough, this change was one of the many, many mandated by the network to make this show less startling). He later ends up as a giant bat monster.
- Herbert Landon dropping in a serum designed to kill mutants himself mutating into a giant, four-armed monstrosity. Spider-Man and the X-Men eventually stop his rampage across Manhattan and "cure" him, however half of his body is still visibly mutated. In one way, it reveals the ugliness inside a man who was a rather handsome figure with a very loathsome prejudice against mutants.
- Spider-Man himself mutating into a hideous, vicious, terrifying man-spider. The change doesn't happen until the very last minute of the episode, but it's still a horrific scene, with Peter's gloved hands mutating into distorted claws before he starts Hulking Out. The Reveal of the new Man-Spider is like something out of a horror movie, with the Punisher, who had been chasing Peter along effortlessly for most of the episode, suddenly finding himself effortlessly manhandled by a towering arachnoid horror. The Oh, Crap! face as he grabs Spiderman's torn, discarded mask and holds it up, realizing what this thing was. And then there's the very last shot of the scene; Man-Spider, lit from behind so he's just a silhouette, with the only features distinguishable being his huge fangs and six glowing blood-red eyes, leaning down in an Eat the Camera shot...
- Man-Spider himself is a pretty horrific concept. A hideous six-armed hulked-out humanoid spider is bad enough, but he's implied to be even stronger than the regular Spidey, he has organic webbing and so can web you from six hands at once, he spits Hollywood Acid, oh, and his human brain is implied to be degenerating. Meaning he may reach a point where he starts treating humans as prey...
- Silvermane aging backward into a baby. Especially horrifying is when he reaches his little boy age, at which he actually starts yelling "Make it stop! Someone please, make it stop!"
- And later on, the Vulture, with his youth-draining tech, sucking the youth out of people, lastly Spider-Man... and also absorbing his mutating DNA, causing him to sporadically turn into the Man-Spider himself, but retaining his full intelligence and power of speech, and then later seemingly permanently being trapped as the Man-Spider for the rest of his life. Sure, he brought it on himself, but still. Fortunately for him, he's cured by an off-screen plot device...
- Peter's recollections of his own origin story. He has a dream in which first his limbs turn red from the spider bite, then he mutates into a Drider, gets flushed down the drain by Aunt May while screaming for help, then washes up in the river, having grown to monstrous size, and is chased by the army who shoot missiles at him.
- There's something subtly disturbing about the storylines involving Hydro-Man — his sheer relentlessness combined with the fact that anything Peter does to him will only stall him for a few minutes is bad enough, but then he dies because Mary-Jane tricks him into spending so long away from water that he evaporates, and Spider-Man just has to say that water is so common that it's possible he'll come back one day, which means a) it's possible that he's still sentient in his evaporated form, b) he might return having learned from that defeat, rendering him genuinely impossible to get rid of. And then he does come back. And it turns out that he and the current Mary-Jane are both clones of the originals, and they both just disintegrate into water.
- More overtly disturbing is the fact Morris Bench is defined in this series as Mary Jane's former Bastard Boyfriend, whom she dumped for being a Control Freak who tried to run her life. And this is the exact same mentality he maintains when he appears; an obsessive, vindictive, controlling stalker who feels Entitled to Have You is scary enough. Add in his vast power and watching him chasing after Mary Jane becomes terrifying.
- Spider-Man's reaction to him watching Mary Jane fall into one of the portals, presumably to her death. He's out to kill Green Goblin. It's not black suit Spidey, being controlled and crossing the lines. It's Peter Parker, having watched the woman he loves die, and wanting to kill the man responsible, literally pushing him toward a portal that threatens to suck him in.
- Not to mention Mary-Jane's fate herself. She spends the rest of the series falling through a wormhole with no escape. And seeing as obvious weeks and months have passed and it still shows her falling, she obviously cannot die in there.
- Though Word of God states that if the series wasn't cancelled, we'd learn that she ended up in Victorian London.
- While he may have been significantly toned down, Carnage was still pretty terrifying. In fact, back when he was just known as Cletus Kassady, he was specifically quoted to have done things even the post wouldn't print.
Chief: Terri, you like your job? [...] Kassidy loves his.
- As the police force are about to storm Kassidy's hideout, Lt. Lee gets a warning from the Chief that perfectly establishes the kind of man Kassidy is.
- A lot of people remember how over-the-top Spider-Man got after being taken over by the symbiote, but the first part of "The Alien Costume" shows how scary a downplayed symbiote!Spider-Man could be.Rhino: All right, I give up. I'd rather go to jail than to be a snitch.
Spider-Man: Who said anything about jail?
Rhino: Huh? I-I don't get it.
Spider-Man: You will. (shoots a webline at a metal door and reels it in) It's like this, I'm through with not getting what I want!
Rhino: What are you doin'? I told ya, I-I-I give up!
Spider-Man: That's funny. I give up, too. (lifts the metal door above Rhino) I give up trying to be a friendly neighborhood Spider-Man.
Rhino: No...! No, you can't!
Spider-Man: Can't I...?
Spider-Man: Get back HERE, SHOCKER!! SHOOOCKEEERRRRRRRR!!! YOOOU CAAAN'T ESCAAAAPE MEEE!! I'LL CHASE YOU TO THE ENDS OF THE EAAAAAARTH!!!!
- The costume acting on its own accord and knocking Rhino over a ledge and down to his death with a tendril. Peter is horrified.
- Narm Charm, Chewing the Scenery and Memetic Mutation aside, the scene where symbiote!Spider-Man gives chase to Shocker can be downright terrifying in the latter's perspective. To see that humble, quippy lighthearted hero who stopped you non-lethally, now wearing all-black, having resorted to one brutal No-Holds-Barred Beatdown after another, and screaming your name at the top of his lungs out of a lust for your blood is downright horrifying. Not to mention, this is a man with spider-esque powers, having gone Drunk with Power: you? You're just a guy with vibro-shock gauntlets.
- When the Green Goblin retakes control of Norman Osborn in Goblin War. We only see a shot of Oscorp in the middle of the night, with Norman Talking to Themself. As he tries to keep his Goblin personality from taking over, his desperate screams pass into a fit of Laughing Mad.
- Spider-Carnage. He happens to be one of the darkest Spider-Man villains ever made and it's not hard to see why. Imagine a Peter Parker who has lost everyone he loved and found out he'd been cloned and was led to believe he was a clone, having gone so insane with rage and grief he decides to fuse with the Carnage symbiote, become a deranged cackling maniac working with the Kingpin (who describes Spider-Carnage as too evil by even his standards), Hobgoblin, and the Green Goblin to destroy New York and take over the world. The New York of his world is literally a wasteland on fire and Spider-Carnage actually plans to set off a chain reaction that will eventually destroy the all of reality and actually succeeds. The Beyonder actually intervened and used almost all of his power to reset time just for the chance he could be stopped.
- When not a Tear Jerker, Spider-Carnage's Heroic Sacrifice is terrifying. He attempts to fight the Carnage symbiote's power, screaming and apologizing before just shrieking for forgiveness, mindlessly opening an imbalanced portal to kill himself. One hell of a way to wrap the show up.Forgive me! FORGIVE MEEEEEEE!!!
Nightmare Fuel / Spider-Man: The Animated Series