The special effects in Stranger Things were achieved through a combined effort of practical effects and computer-generated imagery (CGI).
Having grown up on genre films before computer graphics, it was important to the Duffer Brothers that the horror elements were done practically. They have said that something about the effects being so tangible in the genre films they grew up on, like Ridley Scott’s Alien, John Carpenter’s The Thing, and Clive Barker’s Hellraiser, was especially terrifying to them when they were kids.
The Duffer Brothers wanted to build an animatronic monster because of a lifelong dream of theirs to physically create a monster and bring it to life on-screen. Having grown up on genre films before computer graphics, they wanted to go back to using practical horror elements and using a person in a suit that could interact with the actors in real time. Mark Steger, an experienced actor, performance artist and choreographer, was cast to portray the monster in a suit.
Spectral Motion, a Los Angeles creature effects studio who previously worked with Guillermo del Toro, were brought in to build the monster. They had only about two months to complete the creature, meaning there was almost no room for error.
The process of designing the monster suit began with a laser scan of Steger's body, from which Spectral Motion made a form of his body to sculpt the body of the monster onto. They then installed animatronics to control the head and arms.
Spectral Motion's robotics engineer Mark Strakian designed the animatronics so the movement of the head petals moved in random patterns, never repeating themselves. There were 26 motors running the head which were so loud that Steger had trouble hearing directions on set.
It would take Steger about half an hour to get into the suit, which weighed about thirty pounds. He wore metal stilts which raised him "eight or ten inches." When the head of the monster suit was opened, Steger's face was exposed, which was later replaced digitally with a mouthpiece created by Spectral Motion. On set, the hands and arms of the monster were operated by a puppeteer with a remote control.
Computer graphics for the monster were used in scenes where an actor in a suit couldn't possibly perform the effects required by the script. Aaron Sims Creative, who designed the concept art for the monster, were put in charge of the monster visual effect shots.
The Upside Down
The Upside Down was also created through a mix of practical and visual effects. Many of the vines and growth were actually moving and physical parts. Visual effects were added when they filmed something like a city street.
Special makeup effects company Fractured FX built the prosthetic for Will Byers' fake body as seen in "Chapter Four: The Body" and Barbara Holland’s corpse which was briefly featured in chapters Seven and Eight. They also built the large, yellow egg that the monster feeds on, which was most prominently featured in the Upside Down in Chapter Eight.
- "Stranger Things episode 6: How the Duffer Brothers created their monster" Entertainment Weekly. July 20, 2016.
- "Netflix's Stranger Things: Shawn Levy interview" Den of Geek. July 15, 2016.
- "‘Stranger Things’ Finale: Duffer Brothers Talk Cliffhangers, Death and Season 2" Variety. July 18, 2016.
- "Meet the man behind Stranger Things' terrifying monster" The Verge. August 14, 2016.
- "‘Stranger Things’ Demogorgon: Meet the Man Behind the Upside-Down’s Faceless Monster" IndieWire. August 27, 2016.
- "How 'Stranger Things' Built Its Terrifying Monster" Vice. August 10, 2016.
- "Stranger Things episode 4: How the Duffer Brothers were inspired by Stephen King" Entertainment Weekly. July 18, 2016.
- "Sam painting, in progress, dead Barb for STRANGER THINGS season 1." Fractured FX on Facebook. August 19, 2016.
- "The Egg we created for STRANGER THINGS!" Fractured FX on Facebook. August 19, 2016.
- Comment by Fractured FX on Facebook. August 10, 2016.