Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Nightmare Fuel: Fallen London
Fallen London is a Twitter-powered, largely text based game with clever storylines and and interesting steampunk-ish atmosphere. Some of the descriptions, however, are pure Nightmare Fuel.
What are the Sorrow Spiders? The story goes that spiders drink from your eyes while you sleep. Sorrow-spiders bite off a whole eye. They get their name from the tears that flow from the remaining eye.
Oh, and they don't steal eyes to eat them. They use them as eggs.
If your Nightmares quality reaches five, you will get this event: In the street, you pass a tall, cheerful man with a brisk manner, a stovepipe hat and a row of bright brass buttons down the front of his coat. He winks familiarly as you pass and spreads his hands: eight fingers. You've seen him before. Of course you have. He was beside your bed when you woke this morning. Or were you still asleep?
And this storylet follows you everywhere you go. Except into death, exile, or prison.
And the 'success' of the particular event: 'That night you dream of a tall building lit by cheery fires. A sign reads CLEFT FOR THEE HIDE IN ME. The walls are wrong. The walls are wrong.' Quite possibly one of the most disturbing lines in the game.
Also the Cantigaster. Everything about the Cantigaster. The Cantigaster basically is a mass of poisonous flesh - that Was Once a Man, he got that way due to a Deal with the Devil made by his then-fiancee, the Duchess, after he was bitten by a snake. His life was saved but at a horrible price.
Everything about the Iron Republic. Everything. You can see it right from the description:
Freedom from laws and tyrants. All laws and tyrants, without exception. This place is exceptionally dangerous. You may be permanently changed.
Some of the recurring dreams storylets can be rather disturbing, especially the Is Someone There? collection.
You are standing between two mirrors. Your reflection smiles, so you smile. Your reflection moves its hand, so you move yours. It takes a very long while for you to realise that this is the wrong way around.
The Mr Sacks visits. Ever wanted to see some of the Santa mythos through a spectacularly creepy, original lens?
That night as you sleep, Mr Sacks crouches on your window-sill. His robe is the colour of salt, and his hood is trimmed with red fox-fur. I have brought you gifts, he whispers.
When your Nightmares gets to 6, you start to draw Recurring Dreams cards that cannot be discarded. The only way to get rid of them is to play them, which raises your Nightmares even more. It really drives home how inescapable your nightmares have become.
The Mr. Eaten storyline. It begins with a ravenous hunger in your stomach, and it only goes downhill from there...
Really, Seeking Mr Eaten's Name could have a Nightmare Fuel page all to its own. See the quotes page for some examples. I'll leave another one here:
Consume a Talkative Rattus Faber "Why are you looking at me like that? I knew a man used to look at me like that. Funny sort. Kept a candle in his - " Down in one "Wait no mmf mggl mmmmmfff!" The aftertaste is distinctly sewery, and you're still damnably hungry.
St Arthur's candle. The storylet where you get it implies you rend it out of your own body fat.
The Cave of the Nadir. Filled with a colour man was probably not meant to see, that rapidly robs you of your memories... and causes your skin and bone to grow over your eyes.