Watching the second episode of It: Welcome to Derry, you’d be forgiven for assuming that the Mother Thing, one of the HBO show’s many terrifying surreal creations, came mostly out of postproduction. The parent of young Ronnie (Amanda Christine), who died during childbirth, emerges in a hallucinatory sequence while Ronnie is hiding under her blankets — she finds herself stuck in a strange sort of womb, with her mother taking on the form of the bed. It’s slimy and creepy and wholly fantastical.

And yet much of this was actually filmed on set: The bed was constructed to fit two actresses, with one playing the upper body, and several minute details of the scene were captured closely in-camera. “We built out and slimed up a very disgusting-looking intestine that she got to reach onto,” reveals VFX supervisor Daryl Sawchuk. “That stuff that we photographed was real — the drapery, the lighting, everything in the room was a solid foundation. We went in and withered the mom away and made her more of a corpse, with a dried-out mummified effect, but we had such a great foundation to work on.” They added some extra goo, too.

This was the way of Welcome to Derry. Building off of his two It films, series co-developer Andy Muschietti shared a broad philosophy with the VFX team when it came to developing the look of this prequel. “We’re both big believers in shooting as much practically as possible, trying to get really good photography — he loves old-school practical prosthetics and makeup effects and slime and goo, and stuff that’s very visceral,” says Sawchuk. “There’s sometimes a convenience factor when you can shoot something against a bluescreen and deal with it down the road, but that doesn’t always give the best results. Holistically, there was a great partnership in terms of the creative ideation and how we wanted to approach the show.”

Bringing the action back about 25 years from the 2017 It film, the ’60s-set Welcome to Derry opens on a new family’s arrival in town, the disappearance of a young boy and the birth of a flying mutant baby, whose killing spree kicks things off in bloody fashion. The prosthetics team actually puppeteered the birthing sequence, establishing the unusually on-set method of depicting even the most outlandish sequences.

“You start to see these first assemblies and it’s shocking and it’s visceral, and you’re like, ‘Well, surely there are going to be notes from the studio where this is not going to go to air like on camera’ — but of course it does, and it makes for such a shocking entry into the series,” Sawchuk says. “I thought we’d have to replace the baby with a CG one for the birthing scene. But we ended up using it all practical.” Again, they added some goo at the end for kicks.

Sawchuk credits the production’s ability to employ that “old-school horror film work” style — which is not typical for modern genre TV — with the show’s network. “Even the initial episode of Game of Thrones, where their main character is killed and you’re like, ‘Oh my God’ — it’s such a shocking way to start the series,” he says. “I think on any other platform or with any other studio, there probably would’ve been a lot of notes and maybe a more conservative approach.”

Yet there was also the matter of having the standard of two highly regarded, hugely successful films to meet or exceed. “We put a lot of pressure on ourselves to make sure that we kept up with the photography and the production design and the amazing prosthetic work,” Sawchuk says. He worked closely with Muschietti, who directed half of the eight- episode first season and brought in “very demented and radical ideas” on how to push the designs further. They wound up having an unusual amount of time to devise out-of-the-box strategies, with strikes and other delays ultimately leading to two and a half years’ worth of VFX development on the show. Normally on episodic TV, you get less time than on a feature. Here, they had more.

“Andy almost treated it like an eight-hour feature film, where truly no shot was finished until it was ripped out of our hands,” Sawchuk says. “It just meant that we were able to do extra reps and extra refinements and detailed passes.”

Occasionally, they still bumped against the specific parameters of TV production and needed to get creative: “A lot of what we do is we figure out, ‘Well, how many shots can we afford to do for that amount of money and that amount of time?’ And when things kind of blow up a little bit, you have to figure out how to make those things work.”

The primary vendor that the team worked with, Rodeo FX in Montreal, had also worked on the It films, so they joined the process with familiarity on their starting points — and an understanding of how to take things to the next level. Take the central figure of the It films, Pennywise the Clown, who returns here and is portrayed again by Bill Skarsgard. It’s still the iconic villain we know and love, but subtle changes in the way he’s envisioned and filmed make a notable impact.

“I thought we could do something that was a little more anatomical — we could really play into how as the mouth stretches open, what the orbital bones do, and how that structurally pushes and pulls the anatomical features underneath the face,” Sawchuk says. “We spent a lot of time designing things in as naturalistic a way as possible. As a result, it was a more aggressive-looking Pennywise.”

Sawchuk points to one of the season’s most memorable images, when we see Pennywise almost frozen in place in a chilling tunnel sequence. His eyes are twitching. His physical vulnerabilities are exposed. It’s the same Pennywise — and yet as you’ve never seen him before.

“Andy went, ‘We’ve never been able to be this close to him and really appreciate the slime and the drool and all the details in the mouth and teeth,’ ” Sawchuk recalls. “We knew what the baseline look of the creature needed to be, but we wanted to make sure that we could kind of upgrade and push it to its limits.” Which is to say, in the world of Welcome to Derry: You can never have enough goo.

This story first appeared in a June stand-alone issue of The Hollywood Reporter magazine. To receive the magazine, click here to subscribe.