Robert Pattinson took inspiration for his character by watching videos of televangelists, and pop-stars from the time period.
Robert Pattinson didn't work with a dialect coach and crafted his high-pitched Southern drawl on his own. The actor hid his accent from everyone - including director Antonio Campos - until day one of filming. Other actors sent Campos recordings of the voices they were working on - but not Pattinson, preferring to rehearse by himself and getting self-conscious by being judged before actually standing in front of the camera. Campos called Pattinson a "mad genius who can do anything."
The screenplay was adapted from the 2011 novel "The Devil All the Time" from author Donald Ray Pollock, who also voiced the narration in the film. It was the first time he has done any narrating, not even doing the voice work for his own audio books.
Actor Harry Melling dumped real orb-weaver spiders on his head. He said that he was okay with it as long as the spiders weren't changed to snakes.
Despite top billing, Tom Holland doesn't appear until 46 minutes into the film.