- The Dark Ocean, and the creatures living in it.
- The Divermon in episode 13 who live near the Dark Ocean want Kari to have a child with them. One of them even calls Kari a "virgin".
- During episode 20, Ken starts hearing voices that laugh at him. He even has a vision of himself about to fall into a deep dark hole. Instead of taking a moment to stop and consider what's going on, Ken instead grows more and more maniacal.
- The Digimon Emperor's Villainous Breakdown after realizing the Digital World wasn't a game.
- Oikawa's creepy email to young Ken in "Genesis of Evil"."I'm sorry for the loss of your brother. It must have been hard to take, but don't worry. Your brother is in a better place than this world. He is finally at rest. But when his soul became free, yours became trapped. You will now bare the burden of both his destiny and your own. Now that your parents have lost their hopes for their "perfect child". You will be expected to carry out the dreams that Sam can no longer fulfill. This world will become unbearable for you, the pressure to succeed will be too great. But let me tell you about another world that is much more appropriate... a world where your soul can finally be free, where you answer to no one but yourself."
- From the same episode, young Ken's first trip to the Dark Ocean. He finds himself standing at the edge of the water. Then the audience is treated to bits of dialogue of Ken as the Digimon Emperor as Ken gives in to his anger and places his Digivice in the water, letting the Dark Ocean corrupt it.
- Arukenimon appearing in Ken's room in the middle of the night in "If I Had a Tail Hammer".
- The encounter TK's mom has with Oikawa. A strange, pale man just confronts you in the street and ominously hints that the life threatening events that nearly killed your sons are happening again, before disappearing? Adult Fear doesn't even cover it.Oikawa: Enjoy the holidays, ma'am. It's the most wonderful time of the year...
—>Natsuko: (Thinking) He's gone! What have the boys gotten themselves into this time? I thought this Digital World stuff was over with, now the danger starts again!
- Arukenimon and Mummymon abducting children to implant with Dark Spores. And the children themselves, even before getting the Dark Spores.
Child: Oh, hey, mister. Guess you're all alone too. You wanna be friends?
- What makes it worse is the build-up; Right after some light-hearted action with the Children, we cut back to a playground in Japan; a lone child is sitting on the swings, and when we cut in for a closer shot, Mummymon is there too.
Mummymon: ...(Slasher Smile)
- Oikawa's hallucinations in the cemetery in "BlackWarGreymon's Destiny".
- MaloMyotismon torture-murdering Arukenimon and Mummymon.
- His design is a bit creepy as well, especially his shoulder cannons that open like organic jaws.
- The completely surreal final battle against Cherubimon in Hurricane Touchdown/Supreme Evolution! The Golden Digimentals.
- Diaboromon's return in Revenge of Diaboromon shows that the virus Digimon is just as dangerous as he was in Our War Game, staying one step ahead of the Digidestined and achieving his goal of materializing in the real world as Armageddemon, handily beating Omnimon and Imperialdramon.
- In the English dub at least, the fake Blossomon in the episode where Silphymon debuts. Not only is it bigger than usual- unlike the other Black Tower-created Digimon, this Blossomon never talks or even makes human-created grunts. Oh no- it roars a nightmarish roar. Even In-Universe, this roar actually traumatizes Kari out of digivolving Gatomon to Angewoman, just as she's about to.
- The unexplained apparition of Devimon.
- It actually is explained, just not particularly well. Though that doesn't make Devimon's presence any less frightening. Devimon's appearance in the Dark Whirlpool is a fragment of his former self who the Digimon Emperor hunts down to gather his data to create Kimeramon. The implication of Devimon being here is that either he's been reviving all this time, or that he's spent three whole years alive and reforming after Angemon beat him. And then when his data is used to complete Kimeramon his personality turns out to have survived and his evil influence turns Kimeramon into an unstoppable rampaging berserker that takes Magnamon, a Royal Knight with power on par with a Mega Level digimon, to finally be put down. Even three years later, the original Big Bad of Digimon is still terrifying.
- The end episode 28, where Stingmon pulls a Full Nelson on Exveemon and Digmon torturing the latter with his drills.
- Daemon's entire appearance. A mysterious being with enormous amounts of power whose very presence gives off a creepy Satanic vibe and can only be sealed away rather than defeated. His appearance may have been short, but it sure as hell was memorable.Daemon: The powers of darkness are not to be trifled with!
- From episode 49, Ken's disturbing and heartbreaking vision within his "happy place" of himself as the Digimon Emperor being attacked by several angry Digimon. Followed up by a vision of his late brother Sam, telling him to give up and embrace the illusion.Ken: Huh? Wait a sec, Sam! I thought you were dead!"Sam": I've come back to invite you to stay with me here, where you no longer have to suffer for the errors of your past. I'm your brother. Trust me.Ken: I can't keep these visions out of my head. If I stay, will you help me? Where have you been? I've missed you, Sam.Wormmon: Ken, can you hear me?Ken: Huh? (Ken turns to look at Wormmon, when he turns to look at "Sam" again, "Sam's" vanished) Wormmon, what happened to Sam?Wormmon: He was never really here.Ken: (breaking down) But he promised to help me!
Nightmare Fuel / Digimon Adventure 02