This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Monster House
Plenty of it. Though you probably wouldn't expect anything less from a movie named Monster House.
Just the house in general.. Not to mention the part near the end, when it sprouts legs.
The fact that all the planks cut irregularly when the house turns into a monster is especially scary since those planks are sharp and could tear clothes, or worse, leave bloody wounds, scratches, or splinters. Some scenes that deal with so many of those planks could have been sharp enough to deal fatal injuries.
Whenever the house "eats" someone or something with its carpet-tongue.
It ate a whole car, for crying out loud! Then it tries to eat the kids. Visually, this scene is particularly disturbing because the first scene where the house looks at its angriest and deformed. It wasn't just attacking on instinct, it felt merciless rage towards the kids for everything that they had planned to do to her with the vacuum cleaner dummy and their attempt to report it to the police.
In another unsettling scene in the movie, DJ has a nightmare in which a shadow of a giant hand attacks him in his sleep. The entire room glows an eerie shade of red, and the music intensifies the tension.
Some of the original concept art of the movie reveals that in DJ's original nightmare scene, he was supposed to be inside the house, where he would be walking down an eerie, empty hallway with pipes bursting through the walls.
Another early draft of the movie, Zee, DJ's babysitter was originally supposed to be grabbed by one of the house's trees.
This◊ unused concept art which depicts a deleted scene where Chowder is in Constance's room and her ghost appears to be charging at him while screaming from a mirror.
The house calling DJ on his phone. All he hears is its breathing.
How Nebbercracker was in the beginning. A little girl rides down the sidewalk in silence, stopping at Nebbercracker's for some reason....:/? Then Nebbercracker comes out and screams at her. No explanation behind it at all. At least not until later into the film.
Constance's death by concrete-drowning.
The DVD menu for the movie. It certainly does not look like a menu for a typical children's film. It is night-time, none of the main characters from the movie are present, you hear nothing but a loop of the movie's creepy main theme song and all you see is the house staring at you with an angry face, breathing and growling.
To make things even creepier, if you play the movie and return to the main menu after watching it, the house will randomly switch to its monstrous face and roar at you. Yes, there are jump scares in a DVD for a children's film.
The house's doorbell. Easily the most frightening sound ever to be put in an animated film.
The Video Game:
Everything about the game. It was surprisingly dark for a game with only E+ 10 rating. At times it almost feels like a throwback to Resident Evil.
Constance's mannequin. Its appearance in the GBA version of the game is arguably even worse, as you encounter it several times throughout the game, and it gets more deformed each time you come across it. The music during the boss battle doesn't help this.