According to the Duffer Brothers, this episode has more visual effects than the entirety of Season 3.
Joseph Quinn played some guitar for Eddie's performance of Metallica's "Master of Puppets" himself. In a 4 July 2022 interview with The Hollywood Reporter, Quinn revealed that he didn't play the actual guitar solo because he's not a heavy metal guitarist, but he played the first notes that Eddie shreds after practicing manically for months before the shoot. The actor also had a guitar hand double on set, professional guitarist Aidan Fisher, who shared behind-the-scenes images from the shoot on his Instagram. The lead guitar track was performed by Tye Trujillo (who was 16 years old at the time), the son of Metallica's bassist Robert Trujillo, who is credited in this episode for "additional guitar tracks".
David Harbour lost 60 lbs. for this show and Marvel's 'Black Widow'.
Eagle-eyed fans were able to correctly guess from trailer footage that Eddie was playing Metallica's "Master of Puppets" due to the song's famously extensive use of downpicking.
This episode with 139 minutes marked one of the longest runtimes of a single episode ever. The all-time runtime record of a single episode is for 91. Bolum (2017) (Turkish version), which was 165 minutes long.