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Nightmare Fuel: Home Alone
The furnaces "HELLOOO KEVIIIN!!" Doubles as in-universe Nightmare Fuel for Kevin.
Nullified by the fact that Kevin simply tells it to shut up, and it works.
Buzz's pet tarantula, Harry and Marv to some people, and a few of the booby traps.
Highlights of the booby traps: the nail through Marv's foot, the tarantula, the glass ornament stepping, the scenes with the furnace, and the electric sink. That wasn't Kevin down there in that scene...that was Henry Evans!
When Harry and Marv manage to catch Kevin, they gleefully claim that everything Kevin did to them, they're going to do to him. All those booby traps? Not so funny when you picture those things being done to an eight-year-old boy. Harry even said he was going to bite off all of Kevin's fingers, and had every intention of going through with it. He actually had one in his mouth before a shovel-wielding Marley came in to rescue Kevin.
Home Alone 2
Kevin walking around Central Park at night, for some.
Near the end, when Harry and Marv are standing over Kevin, paint all over them looking like dried blood, crazy slasher smiles...and the line "My, how the tables have turned". Brrrr.
How close Harry comes to shooting Kevin in Central Park - although it turns out that Kevin was in no real danger because the gun was jammed.
Also when Harry first comes up to Kevin in Part 2 and says, "Hiya paaaal!"
And when he rises his hand towards Kevin, revealing the burn in the shape of the doorknob in the first movie.
The Pigeon Lady standing and watching as her pigeons swarm Marv and Harry, especially when she laughs.
Marv getting electrocuted and turning into Skeleton-Marv for a few seconds was enough to scare the crap out of you.
From Home Alone, the wreath of the McCallister residence at the beginning of the movie features a rather mean looking Santa, with his eyes in shadow Fist of the North Star style... and then they zoom in on the thing! Yeesh!