Just so you know, there are definitely spoilers ahead!
1. Stranger Things creators Matt and Ross Duffer, aka the Duffer Brothers, revealed to Rolling Stone that the show was rejected around 15-20 times when they were pitching it. One executive even suggested either focusing on the young characters or Hopper exclusively, rather than combining the two generations in an ensemble cast.
2. The Duffer Brothers told Entertainment Weekly that Millie Bobby Brown, who was 11 at the time, wasn't sure about buzzing her hair to play Eleven...
...until she was shown a photo of Charlize Theron as Imperator Furiosa in Mad Max: Fury Road. The Duffers wrote that they asked their young star, “Charlize looks totally badass, right?” Brown wholeheartedly agreed, and gave them the go-ahead for the haircut.
After it was done, "Millie looked at herself in the mirror, gave her best Furiosa scream — and Eleven was born."
3. Speaking of Brown being only 11 years old during Season 1, Ross Duffer told an adorable story on NPR about the young actor coming to set one day "just covered head to toe in glitter." Duffer said, "And she's like, 'I don't know where this glitter came from.' And it's like I'm not having this problem with any of my adult actors. David Harbour is not coming in covered in glitter." Matt Duffer added that the unexpected sparkles delayed filming by 45 minutes. Ross joked, "I don't know if you've tried to get glitter off someone, but it's very difficult."
4. The Starcourt Mall that's featured throughout Season 3 was built in an honest-to-god "dying mall" in Georgia. Production designer Chris Trujillo told the L.A. Times that the production team recreated around 40 period-specific storefronts in the Gwinnett Place Mall, which he described as being "in a state of almost complete disrepair."
Trujillo said, "Imagine a mall without stores and without decoration. We had to painstakingly recreate the facades, all of the signage, all of the storefront displays. In many cases, we had to reconfigure the storefront architecture because it was in disrepair or it had been piecemeal remodeled through the years."
5. Finn Wolfhard, who plays Mike, taped his audition tape while he was sick in bed. He introduced himself by saying, "Hi, I'm Finn Wolfhard, I'm sick, I'm 4'11'', I'm 12 years old."
6. Dan Cohen, an executive producer, told Yahoo Entertainment that one early idea for the series involved each season being set in a new decade. Cohen said, "At one point, there was this idea of doing ’80s, ’90s, 2000s, and then Season 5 would be 2020, and it would catch up to present-day. But I think, at the end of the day, there was this world that we really loved and in making it, and we didn’t want to move away from these kids."
7. Matt Duffer told Variety that the unlikely friendship between Steve and Dustin formed nearly accidentally as a result of the fact that neither of the characters had much to do, so it made sense to match them up.
Duffer said, "My favorite this year is the Dustin and Steve combination, which actually wasn’t in the initial pitch to Netflix. It was something that kind of evolved as we were writing the show and Steve was kind of getting sidelined. He had nothing really interesting to do. And Dustin found himself cornered with no one to go to, and that led to this Dustin and Steve team up which turned out to be so much fun."
8. Winona Ryder doesn't have children, and she told Marie Claire UK that she turned to her own mother for advice on how to play Joyce Byers.
Specifically, Ryder asked her mother if she would ever believe her child was dead if it happened under mysterious circumstances. Her mother replied, "If you don’t see it happen, you don’t believe it." Ryder said, "It’s a weird, primal thing. But I may have gone too far: It seemed like every day I was crying or freaking out."
9. Ryder took special care to stay hydrated while filming the iconic Season 1 scene where Joyce makes contact with Will through Christmas lights. Shawn Levy, the director of the episode, told Vanity Fair, "For 10 hours, she was depleting her liquids through her tears. It would never occur to me, ‘Oh, you should probably hydrate because all of your water is coming out through your tear ducts all day."
10. On the aftershow Beyond Stranger Things, Millie Bobby Brown revealed that the Upside Down was originally called the "Nether" in the Season 1 scripts.
11. In the book Stranger Things: Worlds Turned Upside Down, Ross Duffer revealed that Eleven wasn't originally going to survive the first season. According to Duffer, "Eleven was going to sacrifice herself to save the day. That was always the end game. But once we realized that the show was potentially going to go on longer than one season, we needed to leave it more up in the air, because deep down we knew the show just wouldn’t really work without Eleven. And at that point, we knew how special Millie was. If there was going to be more Stranger Things, Eleven had to come back."
12. Steve Harrington was also marked for an untimely demise in Season 1. In the same book, Duffer said that Joe Keery's strength as an actor saved Steve from simply being a "giant douchebag" who died.
13. Any fan of the show knows that the Department of Energy is the unexpected villain behind the dastardly treatment of Eleven and all the other bizarre experiments related to the Upside Down. Well, the real life Energy Department isn't quite so sinister, and to let the public know that, they published a friendly rebuttal to the series on their official website.
According to the Energy Department, it "doesn't explore parallel universes" or "mess with monsters." Also, "National laboratory scientists aren't evil — they're actually really nice (and smart)!" A likely story.*
14. Two of the youngest cast members possess seriously impressive Broadway cred. Gaten Matarazzo (Dustin) played Gavroche in Les Misérables...
...while Caleb McLaughlin (Lucas) played Young Simba in The Lion King.
15. According to Vulture, the young cast shared a group message while filming Season 2. What was it called? "Stranger Texts," naturally.
16. Dacre Montgomery, who plays Max's bully of an older brother, Billy, told the Hollywood Reporter that he was a huge fan of the show's first season. So when he heard they were looking to cast someone as an "18-year-old bad boy," he went all-out with his audition tape.
Montgomery said, "I had an opening score, opening titles, and credits. And I got in a G-string and danced naked to ’80s music with this leather jacket and crazy glasses." Apparently, the Duffers were into it, and Montgomery was cast as Billy within the week.
17. Millie Bobby Brown told Entertainment Weekly that her emotions in the scene where Eleven reads the letter from Hopper were "raw" because she hadn't heard or read the letter before filming.
Brown said, "They had prerecorded David [Harbour] and they played it out loud. I didn’t want to read that speech. I didn’t want to hear about it. I didn’t want to rehearse it. I just immediately wanted to put a camera on me and find the way I react and the way I reacted was pure devastation and sadness, and a distraught child that just lost her father or so she thinks."
18. Joe Keery told Entertainment Weekly that when he read the scripts for the first half of Season 3, he realized Steve was wearing his Scoops Ahoy costume the entire time and thought, "Okay, I must change at some point."
Keery said, "And I was just talking to myself, 'Oh, Jesus, am I ready for a billion people to see me in this dinky sailor uniform?' But after we shot the first day, to be honest with you, it grew on me. It really is perfect for the character. It’s such a good grounding tool. You know? You couldn’t ask for something more perfect. So maybe I might burn it at some point or maybe just give it away for charity."
19. Joe Keery told Entertainment Weekly that when he and Maya Hawke (who played Robin) were filming the scene where they were interrogated by Russian agents, they "stay tied together for six hours" because untying themselves for a break would take as long as the break itself would last.
Keery said, "That actually proved to be one of the more difficult sequences, much more than any of the stunt choreography. Tied together was, like, kind of tiring."
20. In Season 2, Joyce's new boyfriend, Bob (Sean Astin), heroically sacrifices his life to save the rest of the group. It is tragic and, according to what Matt Duffer told Variety, it was meant to happen way sooner in the season and matter way less.
Duffer said, "The interesting thing about Bob is he was going to be Joyce’s dorky, boring boyfriend, and then he was going to give Will some really bad advice, and he was going to meet it around Episode 4. ... And then we met Sean, and I kind of fell in love with Sean and his real-life personality, and so we sort of fused him with this character of Bob. It created this character who was so much more lovable and interesting than the one we had initially written."
He added that while Bob dying was "narratively the right thing to do," it was the "hardest scene to write" because neither Astin nor the Duffers wanted to say goodbye.
21. And finally: Stunt coordinator Hiro Koda told Screen Rant that the Season 3 moment where Eleven tosses a show car across the Starcourt food court was achieved through practical effects, not CGI (or telekinetic powers).
