Canadian dancer and choreographer Emma Portner plays four different roles in the film, three of them being villains in The Pink Opaque. She played Marco, the evil clown, and Mr. Melancholy. The only non-Pink Opaque character she plays is Amanda, Maddy's friend who originally began watching The Pink Opaque with her until they stopped being friends. Maddy later says "I feel like she's a secret agent sent here to make my life miserable" after bringing up how their friendship fell apart. The fact that she plays most of the villains in The Pink Opaque adds to the quote.
The Pink Opaque, the fictional television series in the film, was inspired by shows such as The Secret World of Alex Mack (1994), Buffy the Vampire Slayer (1997) and Are You Afraid of the Dark? (1990).
Multiple 90s stars are included in the film. Michael C. Maronna and Danny Tamberelli, known for the Nickelodeon series The Adventures of Pete & Pete (1992), show up for a brief moment. Fred Durst, lead vocalist of Limp Bizkit, also has a fairly significant role in the film. In an interview with Vulture, writer/director Jane Schoenbrun said their inclusions were less about reverence and more about being "haunted" by these familiar faces. They reference these faces being ingrained in their subconscious as a child of the 90s, and how they found it interesting to bring these faces back to the screen after so much time.
Just like the rest of the film, The Pink Opaque segments that appear throughout the film were also shot in 35mm, but later transferred to both VHS and Betamax in post-production to create the show's different period-specific degradations.