Hereditary
Hereditary was a game-changing film, not because of its setting or theme, but because of the writing and acting. If you think you can handle a standard horror film, Hereditary will take that and crank it up to 11 for you.
A Serbian Film
This movie is not for the faint of heart, and it absolutely IS NOT okay for children to watch. A Serbian Film is about an adult film actor floundering for cash, who agrees to work on some movies that forced him to commit horrific acts of violence and torture to his co-stars. This movie is actually banned in seven countries.