25. While Priah Ferguson was intended to only appear in one episode in season two as Erica, Lucas' sassy little sister, the Duffer brothers kept finding ways to add the scene-stealer. She was made a series regular the following season.
26. Given that the younger cast was still growing as the series was filming, the wardrobe department faced a unique challenge when it came to continuity.
"It's crazy," costume designer Kim Wilcox told E! News. "We had one kid we could not keep in shoes, like every three weeks he grew a half-size." Her solution was to find heritage brands that make the same product in multiple sizes. "We'd buy five of them so that when somebody grew we'd have something."
27. While the Duffers were paying homage The Goonies, E.T., and Stand By Me, they were cautious not to be too overt in their references.
"When we billed the project to Netflix, we had this big two-and-a-half-minute trailer that had about 20 or 30 of these movies kind of woven together to try and tell the story of Stranger Things, but obviously all these images or ideas were in our heads," Matt told The Daily Beast. "Those are the movies that we grew up on and they're so much a part of our DNA. But then when you get into the writers' room and you're working on individual episodes, actually very little time is spent referencing other movies. Mostly you're just trying to tell the story, letting the characters guide where everything's going. Otherwise it would just be a jumble and a mess."
28. The creative team set out to use as little special effects as possible to achieve a throwback feel, but quickly learned how difficult that would be.
"The funny thing is that the original goal was to do entirely practical effects. But what we realized—and it really made us admire those guys who did The Thing and Alien and whatever—is that doing practical is really hard," Ross explained. "It takes a lot of time and preparation. We were turning out scripts as quickly as we could but they don't have six months to prep this stuff. You show up on set and stuff that seemed like it would be a great idea to do in that old school way, we didn't have time to do."
29. When they first pitched the show, the Duffers always envisioned a five-season arc. "So much of what they had in their head in 2015 is what we're now seeing play out as we come to the end of this series," Netflix executive Matthew Thunell told Variety, with the magazine reporting that each of season four's episodes cost $30 million.
30. While an ending for Stranger Things has been set, the Duffer brothers aren't ready to leave the Upside Down just yet.
"We do have an idea for a spin-off that we're super excited about," they said in an email interview with Variety, "but we haven't told anyone the idea yet, much less written it."
Despite their efforts to keep it a surprise, Matt and Ross admitted that Finn already guessed the premise of the series, which they described as "very, very different." They added, "Aside from Finn, no one else knows!"