This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / American Horror Story: Murder House
In the pilot we see Violet leading Leah into the basement with the promise of Cocaine. What happens instead is that she gets attacked by Tate and the Infantata.
In "Rubber Man" Vivian being put into a mental institution through Hayden's manipulations and Violet's lying and no one believing her.
In "Smoldering Children", Violet finding her body. There are flies in her mouth and her eyes are rolled back into her head.
In the same episode, Harvey's dead, horribly-burned wife and children acting as though they were still alive.
The school shooting sequence in "Piggy Piggy". Tate meticulously shoots people one by one as they plead for him not to. And then you remember we saw what became of the the Dead Breakfast Club just one episode prior. The nerd's injuries were so bad he couldn't even speak. Damn.
In "Birth", Chad's plan for Vivian's twins once he and Patrick get their hands on them: smothering them when they get at "that right age", so they'll "stay cute forever". Considering Constance is the grandmother of one of the twins due to Tate's raping of Vivian, she's visibly disturbed by this.
Dying in the house is this: You cannot leave for the rest of your dying existence.