When the movie was picked up for distribution, it could no longer be as attached to Inviting the Demons (2013), and had to become more of a standalone movie to avoid audience confusion. This is because Inviting the Demons cannot be released in any official capacity outside of streaming due to legal reasons. The re-editing and reshooting process therefore turned Unleashing the Demons into a standalone movie, which does not require knowledge of the events of Inviting the Demons. However, Inviting the Demons can still be viewed online as a prologue.
At the end of the movie, there is a dedication "For Katherine." This is a dedication to director Callum Knox's auntie, who passed away a couple of weeks after principal photography.
The movie premiered in July 2019 with a temp score attached. However, the score was subsequently rejected, and Pierre Duyker came on-board to compose an entirely new score on a shortened schedule.
Due to a botched haircut, Keiron McDonald's hair was too short when reshoots occurred in October 2019. To get around this issue, Keiron was made to wear a beanie and hoodie on-set despite the warm weather. The hoodie cost $30, as the crew needed to find one without any brand logos, and Keiron got to keep it.
The demon cloaks were purchased from regular costume stores.
Mark Laygan: the production's behind-the-scenes videographer/photographer voices the doctor inviting Derek to come in for his appointment.
Callum Knox: as a detective. This was not planned in advance. All candidates for the role fell through, and Callum stepped in at the last minute to ensure the scene could be filmed. Seeking a last-minute costume, Callum selected a leather jacket to channel Andy Samberg in Brooklyn Nine-Nine (2013).