The Chzo Mythos games are supposed to be scary, and they are. Creepy music, eerie settings, Eldritch Abominations, the lot. But Yahtzee went Too Far in Trilby's Notes, which is set in a hotel which repeatedly shifts to a Dark World version of itself. This happens at random times; the player will be happily traipsing through the Day hotel, try to open a door, and suddenly the message 'it hurts' will appear. On dismissing this message, the screen will fill up with 'it hurts it hurts it hurts it hurts it hurts' and suddenly the hotel goes from a fairly pleasant holiday location to a nightmarish bloodstained hell.
Every time you switch back into the Light World, you have a random chance of a hallucination, seemingly being transported to Cabadeth's cabin or the cargo bay of the Mephistopholes from 7 Days. The one where you are cornered in the basement of Defoe Manor, with John Defoe slllooooooooowwly menacing you as the "You are in grave danger!" music plays is particularly scary. And the only response out of the text parser when you are about to die? it hurts. it hurts it hurts it hurts it hurts it hurts it hurts it hurts it hurts it hurts it hurts it hurts it hurts it hurts
What about the first time we see the Nightmare World?! You're just sitting in the hotel room, listening to the conversation... when suddenly, the room suddenly becomes rundown with the bloody remains of the two people you were just talking to lying around, and the enigmatic Tall Man watching you...
In 6 Days A Sacrifice, you and Janine flee into the living quarters at the end of the day, and the two of you embrace during the night. And what do you see when you leave the next morning but it hurts it hurts it hurts it hurts it hurts it hurts it hurts
Probably the worst part about the embracing scene is that, for at least part of it, John Defoe's consciousness was in control.
It's what the tall man does to people that is really scary. The way he emotionlessly swung that four-headed axe back and forth through an already quite clearly dead sailor... just for good measure?
After the final puzzle of Trilby's Notes when you force yourself to die to prevent Cabadath from being summoned, if you enter anything into the text parser all you get in response is It hurts. Keep in mind at this point Trilby is DEAD.
You can get some quality chills (if that's your idea of a good time) by just thinking about 7 Days A Skeptic from William Taylor's point of view. Let's see... You're already freaked out because you think your first assignment is a bit above you, then some innocent-looking object is brought aboard. Then you get taken over and forced to do horrible things to your shipmates. Then he either tears your eyes out or makes you do it yourself once You Have Outlived Your Usefulness. When you finally have control of yourself again there's pretty much nothing you can do but beg the only survivor to fix it before you turn out to have doomed more than just the one ship.
The scene where you find the de-limbed torso of the meganekko in the vent... only for her to suddenly enter the hallway you are in, while you are still STANDING OVER HER DE-LIMBED CORPSE then leaving without a word.
The Fates Worse Than Death that Chzo inflicted on Cabadath, Theo and the Trilby clone. At least Cabadath and Theo were still able to move around and exercise some agency afterwards. The Trilby clone just ended up trapped in Chzo itself, begging to be killed. In comparison, everyone who was killed by the Welder and the Tall Man were the lucky ones.
Why isn't the Trilby clone also brainwashed? Because pain is much more potent when it's unwanted.
Alternatively, the Tall Manisn't happy in his position as Chzo's right-hand abomination, he merely tries to retain it because he fears that whatever Chzo would do to him once he has outlived his usefulness would be far worse. Not sure whether that's any less horrifying.
The beginning of 6 Days is solid nightmare fuel: Theo is painfully injured and trapped in an underground facility (belonging to a creepy pain-worshipping cult) with no way to escape. And that's before the Tall Man shows up and starts slaughtering people...