- Venom. A hate-filled Implacable Man who will stop at nothing to ruin Peter's life played by Peter's former best friend driven insane by envy and misfortune. The way he goes from the affable Eddie Brock to a murderous sociopath targeting Peter's friends and family is overtly unsettling.
- Curt Connors' transformation into the Lizard, around the time that the good doctor's head implodes.
- Or just a few episodes later when Flint Marko's head explodes after turning into the Sandman.
- Any transformation. Villains either go murderously insane, or find their lives completely destroyed. The Lizard is now a savage, mindless animal that at one point tries to eat his own son. Electro's suit is the only thing keeping his powers from destroying everything. Rhino's costume is fused into his pores and he can never remove it from his body. Colonel Jupiter is driven insane by the spores that gave him his powers. Molten Man can't turn his condition off without a special remote, making him easy to blackmail. Sandman loses his human body and is essentially just a mass of sand with his mind in tact. We were also shown Otto Octavius' harness melted into his spine, fusing his tentacles to his back ala Spider-Man 2. Really, it's pretty disturbing to think how lucky Peter got with that spider-bite.
- Should call it the "Spooktacular Spider-Man" given all the disturbing-looking horror-move style villains. Guys like Venom, Tombstone, Otto's tentacles...
- The ending to the eighth episode of the first season. There's an already creepy mask, shifting (as usual) to the classic, red web. Too bad that both the shifting and the web themselves rhyme with Uncanny Valley.
- The entire alien suit arc (AKA Psychology 101), especially "Intervention." As it goes on, Peter starts exhibiting odd behavior like shrugging off the symbiote controlling his body to take on the Sinister Six, not caring that one of his childhood friends hates him, brushing off his other friends, and even going to Tombstone for work. It takes Flash Thompson calling him out on his behavior to make him realize the symbiote is bad and attempt to get rid of it. And, unlike other versions of the story, it doesn't give up when he uses the bell; it cocoons him (while he's pleading for it to stop) and makes him relive his worse memory in attempt to push him over the Despair Event Horizon and make him bond with it permanently (which it would've succeeded in if his uncle's memory didn't step in).
- The fact that it talks to its hosts via the host's own voice is another level of scary, seducing the poor fool who wears it into doing its bidding. If it's being rejected, the voice gets more aggressive and sinister, as demonstrated when Peter rejects the symbiote for the first time.
- Norman Osborn's treatment of his own son is pretty nightmarish. His general disdain and lack of interest are bad enough, but how he deliberately injures Harry to frame him as the Green Goblin is just plain vile. And according to Norman himself, apparently the goblin formula HASN'T made him any crazier than before. He was perfectly rational and in control when he did it...
- While Norman Osborn is the real Green Goblin all along, Harry Osborn's Sanity Slippage makes it believable that he could be the Green Goblin. When Norman "confronts" his son about the stolen vial of Globulin Green after being "caught" in the Goblin costume, Harry grabs his father and throws him towards a wall with a maniac grin. He is completely unfazed by his leg injury as he walks towards his old man, admitting he drank the vial to be the son that Norman always wanted, before passing out. Harry's crazed state is far more closer to the Green Goblin's personality than Norman's cold-hearted rationality ever was, highlighting just how much of a negative impact his father's abusive relationship had on Harry. The poor kid's lapse into drug addiction for the Globulin Green is a disturbing real life example of the effects and highs of drug addiction and the negative effects they have on one's social life and sanity.
- Greg Weisman actually had a way to include Carnage. What happened? Venom would be captured and experimented on while it was spawning, and its child, after bonding to Cletus, would feed off of Bio-Electricity in a more dark take on the Spider-Man: The Animated Series version of him. That's right, he actually found a way to make Carnage kill without killing and, arguably, make Carnage MORE terrifying.
Nightmare Fuel / The Spectacular Spider-Man