Arriving in theaters this Friday — just in time for Halloween — is Come Play, a new horror movie from writer/director Jacob Chase. Based on Chase's own short, "Larry," and fleshed out into a feature-length film, Come Play follows Oliver (Marriage Story's Azhy Robertson), a young autistic boy who uses devices like his cell phone and tablet to communicate with his parents and classmates. When a mysterious creature called Larry uses those devices to enter the real world, Oliver’s parents (Gillian Jacobs and John Gallagher Jr.) must overcome their own marital strain in order to protect their son.

During this 1-on-1 phone interview with Collider, Gallagher Jr. talked about his love of horror movies, the challenges of working with a practical creature, working in a cramped parking lot booth, his experiences working on other genre-driven films like Mike Flanagan's Hush, and much, much more.

COLLIDER: I really appreciate getting to talk about a creepy movie just in time for Halloween.

JOHN GALLAGHER JR.: The timing really couldn’t be better.

When this project came your way, what was it the most appealed to you? Are you someone who is a fan of the horror genre, or did you just want to work with a really creepy creature?

GALLAGHER: Yeah, I do like horror movies a lot. I’m always looking for the ones that keep me reading, where I don’t know what’s coming. If you get a horror script where you feel like you’re ahead of it, it’s not always so fun. It’s hard to come up with an original high concept in horror, and I thought that Jacob Chase, our writer and director, had done that in such an interesting way.

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Image via Focus Features

The thing that really sold me on the deal and made me wanna sign up was when he told me that they were gonna be using predominantly practical special effects. That’s such a rarity these days. He said, “We’re building a puppet for the main creature. It’s gonna be on set with us, every day. You’ll have something to act with and something to respond to.” That just doesn’t happen very often. It’s a lot easier, a lot cheaper, and a lot quicker to go the CGI route now. But as an old school film lover, I love the texture of special effects from the ‘80s and the ‘90s, when they were doing practical effects and more make-up and creature features. I love that stuff. So, when I found out we were gonna be doing that, I signed on right away.

Is there a difference between thinking it’s really cool that you’ll have this creature to work with and then the reality of actually having this creepy character there?

GALLAGHER: Definitely. The effort and the time that it takes is the thing that you’re not thinking about when you’re getting all excited about working with a puppet. You realize that setting up the shot can be tricky and there’s a certain amount of time that it takes to put the puppet together and to figure out the blocking to the puppet. It takes two to four puppeteers, depending on what is needed for the shot, to operate the puppet. So, once the reality sinks in, it is a little bit like, “Oh, right, this is quite a task. This is a bit of a tall order.” But then, when you’re working with it, it’s so beneficial to actually have something there that you can respond to. It’s great when all of the actors can look at the same thing. When you’re dealing with CGI, everybody has something different in their own head because they’re creating it for themselves in their own imagination. But when you have the 12-foot puppet standing right there in front of you, you’re like, “Well, there it is. Now, all we have to do is just react.”

What was it like to actually see what it would look like in person, and also to see what it would look like in the film?

GALLAGHER: It was great. It was so exciting. What I love about film is how it takes a village. It takes so many people to make even a small low-budget film, let alone a film like this with lots of special effects. I was just so impressed by the puppeteers and by the people that designed the Larry creature and the love and care that they put into their job. It’s inspiring and it makes you wanna go a little bit further.

Is there a difference for you in playing the person reacting to the horror in Come Play versus the one causing the horror in Hush?

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Image via Focus Features

GALLAGHER: Yeah. Whatever the situation calls for, I just love to throw myself into it and make it seem as real as possible. Filming Hush was crazy because, as you said, I was the slasher. I was the main antagonist, so I got to really revel in playing this evil, twisted person. When I’m doing something like Marty in Come Play, I just try to make it as real and grounded as possible and think, “Okay, how would I really react, if I turned around and saw this towering gray creature hovering above me?” You just try to respond accordingly and make it feel real. Ultimately, the more I sell something, as an actor, and the more real it feels for me on set, it’s gonna feel more real for an audience, ultimately. I just try to stay grounded and make it as real as possible.

Is there also a different process when you’re getting cast as a villain?

GALLAGHER: Yeah. Honestly, to this day, I can’t believe it happened. I’m so surprised. I was sitting on my couch one day and I checked my email, and there was an email from my agent that said, “Oh, this director, Mike Flanagan, wants to talk to you. He’s written this film, called Hush. It’s like Halloween. It’s a slasher film, home invasion style.” And I read the script and was like, “Are you sure that Mike Flanagan has the right guy in mind? Nobody asks me to play masked killers.” I talked with him and he said, “No, that’s exactly why I want you for the job. I think you’re a good actor and I do think that you’re the last person that comes to mind when you think psycho killer and that’s why I think it will be interesting.” I was totally flattered that he thought I could pull it off and it was a dream, making that movie. Somebody like Marty is much more my own personal style and speed. That’s closer to who I actually am, as a person. Thankfully, I’m not a psychopath.

Especially seeing everything he’s done since then, is Mike Flanagan somebody that you would like to work with again?

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Image via Netflix

GALLAGHER: Oh, in a heartbeat. He’s a dream and one of the most passionate filmmakers that I’ve ever worked with. We shot Hush in about 15 days of night shoots. It was three and a half weeks of nights, so it was grueling. None of us really saw the sun for almost a month. He edits his own work sometimes. He sets up the shots sometimes. He wrote the script with his then-girlfriend, now-wife Kate Siegel. I think he’s one of the most exciting filmmakers in the genre right now. Jacob Chase is somebody that really reminds me of Mike. They’re cut from similar cloth. They grew up with the genre, they grew up loving cinema, and they have a real encyclopedic knowledge of it. That’s my favorite kind of director to work with.

Having an autistic son in this creates a really interesting bond for this family and it creates an especially deep bond between mother and child. What did you enjoy about exploring this family dynamic and how do you feel about the film having this message, when it comes to autistic youth?

GALLAGHER: I just thought it was so interesting. Like anybody reading the script or watching the film, you might get scared initially that it’s being exploited somehow or maybe it’s not gonna be handled as delicately as it should be, but it became very apparent, quickly in the script, that Jacob knew what he was writing about. And then, of course, I found out after I’d met him that the idea came to him because his wife works with children on the spectrum, so it’s something that he knows a lot about. He knew that it was gonna take a lot of respect and a lot of care and a lot of nuance to handle it appropriately. I just thought it was really interesting. I like grounded horror films. I like horror films that deal with real-life issues. What’s exciting about genre movies is that you can actually raise awareness through them. You can put a lot of messaging and morality into scary films and they’ll hold them and spread some awareness at the same time. I just thought it was a really interesting way to frame the film.

What was it like to also work with Azhy Robertson?

GALLAGHER: Great. Azhy Robertson is a superstar in the making. If anybody saw A Marriage Story, the Noah Baumbach film, they’ll be familiar with Azhy’s work. He was tremendous in that, and he’s tremendous in this. He was eight years old when we shot the film and, by far, is one of the most professional actors that I’ve ever worked with, at any age. He took his job very seriously, had an incredible amount of focus, and an incredible amount of consistency. Being eight years old and playing a child on the spectrum is a heavy load to carry, especially when you’re in almost every scene of the film. I think of myself in almost a supporting role in the film, even though I’m one of the pillars of the family. I guess you could say Larry the creature is the star but really it’s Azhy’s movie. It’s his film and he carried it, and boy did he carry it.

How was it to work in that cramped parking lot booth?

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Image via Focus Features

GALLAGHER: That struck me, when I first read the script. I was like, “Okay, now this is a great idea.” I feel like everybody in the film is dealing with their own isolation and my character’s isolation happens to be feeling estranged from his family and also being forced to take this job as a parking lot attendant and toll booth operator on the night shift when nobody is really there. I thought that was such a great idea. We filmed it at night. It took a couple of nights to shoot those sequences and it really was just me and Jacob and the crew. They built this booth on a big stretch of parking lot, and they built it to scale. It wasn’t bigger than a booth actually would be, so we were definitely all jammed in there, from time to time. They could take the windows off for certain shots but for a few nights there, I was definitely crammed into that booth for hours on end and I loved it.

A lot of people continue to look back at Short Term 12 because of the cast and also to see the early work of its filmmaker, Destin Daniel Cretton. What is the legacy of Short Term 12, for you?

GALLAGHER: Oh, my gosh, I’m probably just about the most proud of anything I’ve ever done as I am of that movie. You’re lucky if you get one or two "Eureka!" moments, as an actor, where you just know, right off the bat, that something is incredibly special. That’s what Short Term 12 was for me. I remember getting the script and getting maybe 20 to 30 pages into the script and I was crying, which just never happens. Screenplays tend to be clinical documents because they have to be these blueprints for the film and they don’t always get written with like a ton of emotion or love or flowery prose. Destin Cretton had written this script that was so raw. I just thought, “Wow, if I’m crying and I’m not even to the halfway point of this script, then this has to be something so special.” I remember calling my agent immediately and saying, “I’m not even finished with the script but I have to meet this filmmaker. I think this movie is gonna be huge. Even though it’s not gonna be in every theater and it’s not gonna be a blockbuster film, by any stretch, but the material is so strong.” It’s so wild to see the path that everybody from that film has taken. When we were making the movie, we had no idea that in seven or eight short years, two of the actors would have Oscars. It’s pretty incredible. I feel so lucky to be a part of that one.

You’ve done a few horror projects that have all dealt with different themes, from Hush to Come Play to The Belko Experiment to Underwater. Does it surprise you every time you read a genre script that’s just so different in what it explores?

GALLAGHER: Yeah, that’s what I love about it. If you look at something like Come Play, you’re like, “What’s it about?” Well, it’s about a creature that comes out of a little boy’s smartphone but it’s actually about loneliness and isolation and technology and familial strife. And then, you can look at The Belko Experiment and say, “What is it?” It’s a battle royale at a big company where everybody has to kill or be killed but it’s actually about character and humanity and doing the right things. I just love that about horror movies. If they’re good and they’re well-made, then they’re never just about what they’re about. That’s what I think is so cool about the genre.

If there was a monster or creature in your phone, based on how you use it, what form would it take, if it came out of your phone and escaped into the real world?

GALLAGHER: That’s a great question. It would probably be a WebMD monster that somehow was made up of my paranoia and my fear about Googling the latest condition that I’m convinced I’ve come down with. It would be a WebMD monster. It’s particularly apt right now.

Without spoilers, how did you feel about the ending of the film? When you learned what the ultimate outcome would be for this family, how did you react to it?

GALLAGHER: It’s very bittersweet. I was so surprised. The last 10 pages of the film take some crazy and wild twists and turns that I didn’t see coming. Jacob sets a lot of things up so smartly that you find yourself unable to predict the outcome. I think audiences will probably feel the same pleasant surprise I did from the bittersweetness of the ending. It’s not perfectly wrapped up with a bow and not everybody gets everything that they want but there is this one last strange and spooky surprise that I don’t think anyone will see coming.

Come Play arrives in theaters on Friday, October 30.

Christina Radish is a Senior Reporter of Film, TV, and Theme Parks for Collider. You can follow her on Twitter @ChristinaRadish.