- The state of the Digital World due to all the data being stolen to fuel Lucemon's resurrection. It looks like a fruit with multiple bites taken out of it and eventually corrodes into nothing but a black void near the end of the series. Worse is Luceman planned to do the same to the Earth.
- When Takuya turns into his Beast Form for the first time in episode 11, he turns into a mindless berserker, even lashing out at his teammates and comes within an inch of killing Tomoki. The horror in his voice is clear even in the English dub where while his voice is calmer, it's clear the realization of what happened is a true kick to the gut and it's no wonder he's terrified of his Beast Form for a while after that.Takuya: (coming back to himself) Tommy?...What did I just do?
- From episode 21, Kouji Taking the Bullet for Takuya when his plan for Duskmon ends in Punch! Punch! Punch! Uh Oh... was already bad enough, given that he not only returned to human form but also was passed out from the pain but in a following episode, Kouji is clearly holding his ribs while trying to rescue the others, meaning that they are at the very least badly bruised and probably worse since his breathing is slightly off as well.
- Mercurymon is pretty nightmarish considering he essentially uses his reflection powers to Mind Rape the heroes with Hannibal Lecture after lecture by playing on the insecurities and personal demons to push them into the Despair Event Horizon and nearly succeeds if not for the Power of Friendship and Heroic Willpower displayed by each hero.
- The climax of the Mercurymon arc has Mercurymon nearly killing Takuya and stuffing his body into a coffin.
- Icedevimon is In-Verse Nightmare Fuel considering he's the Digital World's equivalent of a serial killer who went on a rampage killing and feeding off the data of Digimon until he was captured by an army of Digimon warriors. Not even Cherubimon could destroy the guy and decided to simply seal him away forever under his hideout. Not to mention he's a total Sadist and Combat Sadomasochist who delights in killing as many people as possible in the most horrible way possible.
- As hilarious as his voice acting is, there's just something chilling about how playfully murderous IceDevimon from episode 36 is. Even worse, his dialogue implies that those... things in the basement of Cherubimon's castle were the result of him feeding on the data of Digimon that he captured.
- Duskmon is actually a Deconstruction of the Adventure series. Take a random human child with strong emotions, drag him into your world against his will, and make him fight for you. The logical conclusion? He turns into an insane Blood Knight. Not to mention he's the in-verse nightmarish Implacable Man who takes down the heroes with no effort and tanks all of their attacks. He ends up being so overwhelming he nearly drives Takuya into a total Despair Event Horizon and actually makes him consider running back to the real world and leaving his new friends behind. The heroes' survival against him was nothing less than a miracle.
- Lucemon's voice actor in the English dub voiced Izzy in season 1 and 2. For anyone that grew up with those two seasons, they'll recognize that voice anywhere when they hear it in any other character in the later shows. But with Lucemon, they go even further, giving him a more evil tone that's very disturbing. You're basically listening to an evil Izzy at this point and he's ready to destroy the world for fun.
- '''You must choose to follow me or be destroyed'''
- Lucemon's entire entry into the human world is nightmarish. Just opening the gate between the two causes an unnatural storm and levels several large buildings. When he actually enters, everything around him turns into digicode, and considering what happened to the Digital World, there'd be a total extinction of life if he roamed free.
- Everything related to Sephirothmon: A big set of giant Eyeballs, taking the form of the Tree of Life, keeping the heroes inside dimensional pockets, making them confront their own fears, and letting in Cherubimon henchmen to finish the job. But in the end, his true scheme was learning everything about the Digispirits techniques and copy them, alongside Cherubimon henchmen techniques. The only way to defeat him was improvising new techniques.
Nightmare Fuel / Digimon Frontier