- Castle Oblivion itself. The outside architecture is bizarre and off-putting, the interior design is incongruously stark white despite the castle's abandoned state, and each of the rooms look exactly the same when not altered by map cards. The ominous music in the background intensifies how unsettling the building's design is.
- Sora slowly losing all of his memories, specifically replacing Kairi — one of his best friends — with Naminé, was rather disturbing. The depth of his brainwashing was made most explicit when Sora begged Naminé to break his heart to save herself, knowing that she'd been manipulating him the entire time and that he'd probably end up catatonic, staring at nothing just like the Riku-Replica.
- The whole concept of losing one's memories the further into Castle Oblivion they go is pretty heavy Nightmare Fuel all on its own. Sora's gradual descent into madness just makes it even worse.
- Up until the Reveal, some of Sora's "memories" of Naminé have an ominous feel to them. He claims that she "suddenly moved away" and that the adults knew why, but he was too young to understand what they were telling him. Then Riku Replica appears and tells Sora that Naminé hates him and it has something to do with why she moved away. None of the implications there are good, but fortunately, it all turns out to be fake anyway.
- When Riku Rep. was brainwashed to think he was the real Riku, even though he was happy with the way he was. We don't see it either...we just see his speech box saying "No!!" It was really unsettling and sad. He was very forcibly brainwashed. It almost seems like something else for a bit...or that he had to be beaten into submission. The poor guy... Arguably worse in the remake, as the jump-cut occurs right after Larxene slams him against a wall. The looming shot before Riku Rep.'s Big "NO!" is reminiscent of vultures about to dine on a helpless dying animal.
- The Manga gives us the delightful scene of Larxene dragging Repliku to Namine's room, slamming him on the table and telling Namine to make his memories like that of the real Riku. Then saying "[she'll] give him a wonderful memory!", showing Namine wearing a worried face, Larxene's hand on Repliku's head and a sound bubble with a "zap" effect, implying she sent electricity right to his brain! At least he's still alive, but still!
- What about Namine's ordeal? Unlike other Nobodies, who were born in Twilight Town, the poor girl had the bad luck of being born in a huge, intimidating-looking castle that houses no one else except for a comatose boy whom she can't even locate. She had no one to talk to, nobody to form relationship with, and immediately after that, she was taken prisoner by a bunch of adult men (and one sadistic woman) who psychologically torture her by making her hurt someone she never met under the threat of her safety.
- Vexen's death, no matter which version:
- The original GBA version has Axel cutting his throat from behind.
- The PS2 remake/PS3 HD ReMIX versions have him gloriously burned alive.
- In the manga, we're treated to a glorious two-page spread... of Axel punching a hole through Vexen's chest.
- Vexen's death became even worse when Dream Drop Distance reveals that Nobodies can regrow hearts and experience emotions given enough time, meaning that Vexen could very well have been genuinely terrified at the thought of dying. The same game alleviates this by revealing that Vexen was restored to his old self after his "death," and considering what Xemnas originally intended for the Organization, Axel practically did Vexen a favor.
- Zexion's death occurs offscreen in the original version, but in [Re:CoM] we see it in full, with him begging the Replica for his life and slowly going limp, dangling like a hanged man as the life is drained from him.
- How about that scene where Aerith flat out tells Sora that she doesn't exist? And Goofy and Donald don't see her?
- Marluxia's third form looks like something straight out of a horror game; the music and the arena we fight that thing in doesn't help either.
- Given what we learn in later entries, what the Nobody-like thing that he fuses with for both his forms are a mix of this and Tear Jerker.
- Oogie Boogie's pre-Boss Battle cutscene, where he drinks the "true memories" potion... and something suddenly gives him the mother of all Oh, Crap! reactions.Oogie: Agh! What's this? What... Something's wrong! Something deep inside me. Something...scary!Oogie: No! Get back! Stay away from me!
Nightmare Fuel / Kingdom Hearts: Chain of Memories