At the time of shooting, the lake featured in the first episode was not frozen.

Even when the lake did freeze over it was decided that a CG version was visually more interesting.

“Because the production shot over a number of seasons, we were aware of the weather and the challenges it would bring,” notes Piccioni. “There were days where we shot scenes that needed to be in the snow followed by ones that didn’t. The special effects team would shovel snow in and out. We had quite a bit of CG-enhanced snow as well. The big sequence that opens the season takes place on a frozen lake, but the on-location lake wasn’t frozen at the time.” The decision was made to produce a CG version utilizing the HDRIs, reference photos and the same sky. “We had to decide how reflective and how much snow should be on the lake. It turns out when lakes freeze and then there’s snow, it’s a complete white blanket. Even though the lake did end up freezing later during production, it wasn’t that interesting to use. “The biggest thing that we had to do during prep,” Piccioni continues, “was mentally piece together where all of the locations were, how they were going to overlap with each other, what the time periods were and what the seasons were going to be. We had a big board [of cues]: ‘This is where this scene goes, and it’s in this time period. We have to go from here to there. What does that mean? How do we transition?’ Those were the big things that we had to go along with. We would sit in the room with the directors and ADs, try to map out everything as the scripts were being written, and tried to figure out all of the permutations for every change we wanted to make.

A plate of a forest used for a massive fire that takes place.

“In the fifth episode there’s a forest fire, so most of those skies were enhanced and replaced to feel the smoky claustrophobia of what was happening in that town. … All of the birds are CG, and there are a lot more of them as the season progresses. They’re a combination of hero CG fully-rigged feathered birds and some particle flocking in Houdini.” —Jason Piccioni, Visual Effects Supervisor, FuseFX

All the atmospherics, such as smoke and fire, required extensive simulation work by FuseFX.

“In the fifth episode there’s a forest fire, so most of those skies were enhanced and replaced to feel the smoky claustrophobia of what was happening in that town,” remarks Piccioni. “The rest of it is New England in the winter.” Crows were digitally added. “All of the birds are CG, and there are a lot more of them as the season progresses. They’re a combination of hero CG fully-rigged feathered birds and some particle flocking in Houdini.” As for the tiny furry creature that The Kid (Skarsgård) appears to telepathically drive to its demise, no CG was needed. “That was a real mouse. It was three hours of watching this poor woman on the floor making funny sounds to get her mouse to run across our prison set. We used a dummy mouse in the trap.” Visual effects assisted with time-period transitions. “There were a couple of times, especially in the first few episodes, where we were trying to get the camera to take us into these little vignettes of Castle Rock to show what happened in this town and why it might be so cursed,” explains Piccioni. “The town is a character. We didn’t want an on-screen transition. We wanted to be in one room, like in Molly’s house, Steadicam our way out of the door and be in a different room – but it’s daytime and 50 years in the past. We used some compositing tricks, as well as poor man’s motion control, to seam together a couple of Steadicam passes and make them feel like they’re one piece.” Blood and gore were meant to push the story forward. “In the second episode in the montage, with the mascot committing suicide by jumping off the high school, there was a lot of art direction about the blood on that one,” Piccioni relates. “We didn’t necessarily have an agenda to make things super gory or not.”

Because the actual cliff was too dangerous for cast and crew members, it was shot on a greenscreen stage.

The edge of the cliff was created digitally, which allowed for it to appear higher than in reality.

“The warden’s suicide was on our first day of photography, and we launched a car off a cliff. Just once, thankfully. That cliff is shot in a rock quarry which is a small pond, and we did some CG water and matte paintings to make it feel like it’s part of the larger Castle Lake, which we’ll see later in the story. It’s also a dangerous cliff, so we had a duplicate of that on a greenscreen stage for when characters got near the cliff edge.” —Jason Piccioni, Visual Effects Supervisor, FuseFX

A digitally created wide shot of the cliff is made to appear even more perilous and epic.