*Spoilers ahead for season 3 of Stranger Things

Dacre Montgomery's Billy Montgomery does a lot of horrific things in Stranger Things after becoming host to the monstrous Mind Flayer. But nothing can quite compare to the horror that I and a few other assembled journalists felt when the actor walked on to the set last year with a completely shaved head. "No, this is fresh. This is just a decision of mine," Montgomery said, assuring us that the Duffer Brothers didn't shave Billy's hair, so perfectly permed I think it has its own IMDB credit.

But still, this isn't the same old Billy. After being introduced in season 2 as a menace to the core crew of kids but not quite a Big Bad, Billy goes full supernatural force here. The season begins with the local lifeguard being infected by the presence of the Mind Flayer, the evil presence from the Upside Down dimension that's been plaguing Hawkins since season 1.

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Image via Netflix

"I don't think [Billy] is just bad, I think it's pure evil, to use a cliché," Montgomery said about his newly-possessed role. "He's like pure evil this season, but the supernatural element that's incorporated makes it really interesting and makes it dark and at times horrible, but I hope that the choices are interesting and diverse."

To get into the headspace of a sick individual, Montgomery did his horror homework. From the beginning, he looked to one of the best ghost-fueled breakdowns in the history of film, Jack Nicholson as Jack Torrance in Stanley Kubrick's The Shining.

"[I looked at] Jack Nicholson going into it was, not so much as a character but an actor. Some of the characters that he plays like his character in The Shining, for example, was what was tossed around a lot with the Duffers coming into season 2," Montgomery said. "But I think more so with Jack's unpredictable choices that make him an interesting actor. In the second season, I like to think that we started to introduce some of that. But in the third season, it truly becomes more of his character in The Shining. It was extremely fun to play with and very powerful."

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Image via Netflix

The actor also mentioned titles like Hold the Dark and The Haunting of Hill House—gotta' love that Netflix solidarity—most specifically Hill House's landmark sixth episode, which utilized a single funeral parlor setting and only about three camera cuts. That filmmaking magic mingled with, in his words, "really interesting violence that kind of sweeps you around", prepared Montogomery for a particularly grueling Stranger Things season 3 scene that he described as "the most rewarding week of my career as a struggling actor."

He described the production, directed by Shawn Levy, like this:

"We shot a 25-page scene in four days. We kind of locked ourselves in the space, which I'll leave unsaid particularly what it is, but we locked ourselves in the space and we workshopped with Shawn, "could we do this choice, could we do this choice, could we do this?" All on a very high emotional level. And I don't feel like for a second, for her or myself, it was hard. I think it was just like, "Can we do this, can we do this, can we do this?" Then we get into that space and that world and then just go for it and give it 150 percent. It was almost like a closed set because it was such a small space, there was probably four or five people in the space. Shawn likes to get away from the monitor and come into the space, so six people."

We were talking to the actor a year before season 3's premiere, but having watched it now I'm pretty sure he's describing the particularly brutal end to episode 4, "The Sauna Test". It's a showdown between Billy, Eleven, and the rest of the crew inside the local pool's locker room, a sweaty, horrific fight that definitely cranks the cast involved up to the limit.

"We were covered in cuts, bruises from the wirework and the stunts," Montgomery remembered. "And my whole body is covered in bruises. But we were just crying with happiness by the end of it because it's like if I told my 10-year-old self this is you in 12 years, I don't know what I'd think."

For more on Stranger Things 3, check out all our coverage right here.

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