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Spoilers ahead for the entire third season of Stranger Things.

Just when we began flirting with the idea that Billy (Dacre Montgomery) could redeem himself from becoming Hawkins’s resident sociopath, Stranger Things 3 revealed an even more sinister agenda for the horny-mom magnet. Introduced spending the summer of 1985 seducing impeccably eyeshadowed women, Billy doesn’t even make it through one single episode before becoming the unwilling human host for the revived Mind Flayer, a horrifying metamorphosis that sends him into a deep, murderous spiral, and solidifying his status as the season’s Big Bad in the process.

That is, until the finale, when in a moment of self-actualization fueled by fond memories of his mother, he shockingly sacrifices himself to save the town and its inhabitants from further paranormal destruction. Billy may have been gruesomely pecked to death by tentacles for his betrayal, but at least we can now look back at his character and think, hey, he wasn’t totally an evil dude. Maybe he was even a tragic hero all along.

Eager to learn more about the making of Stranger Things 3, Vulture called the Australian-born Montgomery over the weekend to discuss, among other things, the art of a good scream, why he did his own stunts, and how he’s been low-key wearing a wig this entire time.

I was kind of hoping Billy would have a similar character trajectory as Steve did — transforming himself from a bully into everyone’s honorary dad. How did you react when you realized Billy would not only still be a dick, but also literally possessed by evil the entire season?

I loved it. I’d argue that Billy has quite a redemption in the end. He’s a misunderstood character, if you think about it. I really enjoyed this dynamic of playing two wildly different characters — one is misunderstood, and the other is trapped on the inside of a body as “Flayed Billy” or whatever you want to call it. It was incredibly difficult to portray, but I still loved it.

You spoke in the past about how you requested that the Duffers humanize Billy a bit in season two with his abusive father, given that a villain can’t just turn into a villain without a sensible backstory. How did you want to humanize him in this season?

The main element was Billy’s biological mother. That was something I was insistent of having included, to add to his backstory and to see the pain his mother caused him by leaving. That scene with a younger Billy on the beach, it’s just heartbreaking. Billy’s mother hadn’t really been explored last season, unlike his father, but I really wanted to get a glimpse of her. It’s a credit to the Duffers’ collaborative nature that they included it, and that they even let me pitch ideas.

Billy tortures the hell out of everyone when he’s possessed, but his beef with Eleven is different, given she has to be defeated for the Mind Flayer to achieve total dominance. Did you and Millie do some prep work together to better understand the motivations of your characters? Or just to get more comfortable with one another, given the intensity of the scenes you share?

God, yeah, it was really intense. Most of the scenes I’m chasing her as opposed to working directly with her as two actors paired together, but it was still a significant mental challenge. Millie and I gave 200 percent in every scene we did together. It was easy to meet each other with that level of passion in the moment. While filming that final scene, we would scream at each other between takes to warm each other up, just trying to be emotionally connected the entire time. We were giving and receiving all of those emotions, and it was like that for the entire season. And we would both comfort each other after those moments. I would reassure her that we’re safe, we’re gonna be okay, and that I’m not gonna actually hurt her.

Did you lose your voice from screaming so much?

Nearly every day! [Laughs.] Even if there’s no screaming in a certain scene, I’d scream between takes, and so would Millie. We’d scream at each other until we cried. The ultimate professionalism!

I’d like to bring up a few separate scenes of yours. How hot was that sauna Billy was trapped in, and was it as exhausting to film as it looked?

It took a week to shoot that scene. I think that kind of scene is every actor’s dream. It’s up and down, up and down, with the emotional complexities. I lost my voice the most after all of those days — taunting the kids, screaming at them, crying at them, transforming into evil in front of them. To play a polar opposite version of a character from the previous day to the next day is very fulfilling. Thankfully, the sauna itself wasn’t hot, but it was filled with some steam and I had a lot of lip gloss on my face to make me look sweaty.

How many times did you have to be dragged into that abandoned steel plant pit?

Three times on a cord. I was on my chest being dragged, and it was freezing in Atlanta when that scene was filmed, so it was nice to be dragged and be moving to get some heat. [Laughs.] I love all that stuff, because I really enjoy doing all my own stunts. I’m at an age where I’m in good shape and not too much of a health risk for Netflix’s insurance people. That’s part of the dream — doing my own stunts! I grew up admiring stunt choreography, so I wanted to learn how it would be possible to do that, since this season has so much more action than in the past.

What was the most fulfilling stunt that you got to do?

You know in the sauna when I go up to that little glass window, and I spit on the window? The previous take — and this wasn’t in the script — I actually headbutted the window. It was super thick, and my head went through most of the glass. The kids’ reactions were horrified. Imagine my disappointment when that take wasn’t used. [Laughs.]

What was it like filming your terrifying death scene in the mall? What subbed in for all of those tentacles?

It was long and hard. [Laughs.] My fight with Millie aside, on the days we shot that scene with the Mind Flayer, I was being poked with a long stick with balls as the tentacles. It was interesting from an actor’s viewpoint: When I filmed Power Rangers, almost everything was being assisted by a green screen, but it wasn’t the same with Stranger Things. You still get to use your imagination, but it’s a different facet of acting, especially in this contemporary era. You’re imagining things that aren’t there. The great thing about the show, though, is that Netflix had enough money to provide us all with prints beforehand of what the monster would look like, in and around the space where we were shooting in the mall. So I had those visuals in the front of my mind when we filmed — how the monster would move when I was being attacked by it.

Was it easy for you to unwind after filming so many tough scenes? Did you have any go-to self-care routines?

I have the same wind-down routine when I go to bed, whether I’m shooting or not. It’s nothing too special — maybe some TV, maybe a book. It’s more difficult for me to get into a character in the lead-up as opposed to leaving it. Especially with this kind of character, you can’t take it home to your partner or your family or your friends. You’d lose everyone or you’d become progressively more fatigued throughout an eight-month shoot. There has to be a complete separation. You have to be able to switch it off. If not, you’ve got a problem. I was in hair and makeup for so much time during this season, too, that it was easy to decompress in the chair.

Will you miss having to keep your hair so long and permed?

That actually wasn’t my hair! Would you be surprised if I said it was a wig?

Yes, I would!

That wasn’t my hair at all. I guess that’s the sign of a good wig! In season two it’s my hair on top and a wig on the side, but this season it’s all wig. It wasn’t too inconvenient. It’s an amazing piece of craftsmanship, especially since I’m being dragged and beaten around so much.

How would you like Billy to be remembered, given his ultimate sacrifice?

I really hope people will associate Billy with what he did in the end. I really tried to humanize him as much as I could, especially with what I was able to get included about his parents. I tried to empathize with him as much as possible. It’s hard, but he’s a human being. We all have elements of good and bad in us, and to successfully portray such a conflicting personality was a rewarding acting challenge that doesn’t come around too often.

Also given that dead characters find ways to appear in Stranger Things again with flashbacks and such, if Billy were to return in season four, have you thought about how you’d like him to come back?

I’m happy not to return. It’s been an amazing journey for me and this character, and I trust the Duffers know that the end is the end. This season for me was a young actor’s dream. To be honest, I’ve put Billy to bed in my head. I’m excited for the future, and couldn’t be more excited to move on and show people what else I can do.