Nightmare Fuel / Unus Annus

• "Ethan Explores Mark's Haunted Basement" was pretty damn creepy, especially when the "radio demon" made its presence known.
  Ethan: That is the most horrifying noise I've ever heard! Over.
  • In the "Goodbye" livestream, Mark confirmed that they honestly had no idea why the radios were making those noises and that none of them were staged.
• The Melon Man that Ethan became in "Crushing Watermelons Betwixt Our Mighty Thighs". Especially when he went into his bathroom and ripped the melon open in his shower, all shot in a sickly green light.
  Ethan: Who sees the man into the light of day, who keeps the melon to the melon's man? Well, the Melon Man can! Who is the man... the myth... The Melon Man! (Drops the melon on the shower floor) The Melon Man! The Melon Man! (Rips the melon open) The Melon Man! Ahahahaha!! I am the Melon Man! I've done what Melon Man said he could do! This is my man, and this is my melon. Thank you for your sacrifice, Melon Man. For I will now become you! Melon Man! (Feasts upon the carcass of the slain watermelon) The Melon Man... The Melon Man... I am the Melon Man. The Melon Man is who I am.
• In general, Ethan can be surprisingly creepy. Case in point: "Making Our Own Sensory Deprivation Tank", where he appeared to drown Mark, all while being disturbingly serene.
  Ethan: Do you feel relaxed?
  Mark: Less by the second, actually.
  Ethan: That's how — you have to slip into it. It's an eeaasy little drop... Think of it as... drifting off to sleep. The most restful... sleep you've ever had. What's the most restful sleep you've ever had?
  Mark: Uh... any other sleep but this one!
  Ethan: That's right. So... you wanna just sink, lower and lower, into the best sleep you've ever had.
  Mark: Okay...
  Ethan: Alright, don't worry about a thing, just keep breathing... even if it seems like maybe you shouldn't, just breathe in... and breathe out. [Mark does so] That's right. Don't make a peep. Everything will be A-OK. Everything will be A-OK. [Mark starts twitching spasmatically, as Ethan looks at the camera and smiles sweetly]
• In "Reacting to Your Hilarious Green Screen Memes", one of the memes was of Ethan killing Mark in a fistfight, running away from the police, and going insane in the prison he’s sentenced to. Surreal Horror indeed.
• In "Mark Knows What Ethan Did", Mark reacted to some footage from a previous episode "Grip Strength Test: Loser Becomes the Winner's Butler for a Day". Mark lost, but the footage showed that Ethan's grip was loose. What made this Nightmare Fuel is that Mark was in a Room Full of Crazy with pictures of the loose grip hung up everywhere. The whole time, Mark was repeating that "the grip was loose", and how Ethan was clearly trying to trick him. When Ethan came into the room, he seemed genuinely unnerved and terrified, as if Mark really had lost his mind.
• At the end of "Making Snow Cones With Literally Anything But Normal Flavors", Ethan starts giving the video's outro, but soon transitions into rambling nonsense about shaved ice to no one in particular. After a while of this, Mark starts to get worried that Ethan's come down with something and calls a hospital to get help, all while Ethan continues to incoherently prattle, and it gets surprisingly tense... up until Ethan breaks the fourth wall to ask if the bit is over.
• In "Recreating the Miracle of Childbirth", Mark's turn of doing exactly as the title says involves him putting his head and arms in a rubber casing. Once it's time for him to "be born", Ethan begins to sing "Rock-A-Bye Baby" as Mark struggles to break free of the casing. Ethan's singing gets more and more distorted as it goes on, and the sight of Mark's face and hands pushing out of the casing can easily evoke the image of some sort of ghoul or demon trying to get out. As if that wasn't bad enough, this image was also the episode's thumbnail.
• SCP Amy, the end result of "We Accidentally Made an SCP While Amy Was Away", is a genuinely unnerving statue made from various props, most notably a green mask of a human face, that stalks Mark and Ethan across several videos after its creation and constantly makes a loud static noise whenever it's around.