I liked that movie a lot, but does it count as horror? It felt like suspense to me and it was predictable that the protagonist wins at the end by killing all the psycho family members. Plus, it ends on a comedic note.
If they kept the alternate ending, I think it would help the argument of it being horror.
Edit: Heriditarys scene at the end with the daughters decomposed head, the headless mother and headless grandmother was fucked up, in the best sense of the word for horror. If nothing else, I did not see any other movies that were overall as disturbing.
If Hereditary is horror Get Out is ---
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