The house on fire in the clown montage is not an effect. The cast and crew were on their way back to base for lunch when a couple of them noticed a "flicker" off down the road. They immeadiatly turned around and called the fire dept while checking the house for inhabitants.
A small town in Ohio shut down main street so the filmmakers could shoot the scenes of the young group of friends walking around an empty and abandoned town.
Inspired by a real-life incident in which people made up as clowns terrorized the residents of Bakersfield, California around Halloween in 2014.
The cast members did the bulk of their own stunts.