Mike Flanagan said the film takes inspiration from the Batman: The Animated Series (1992) episodes Feat of Clay: Part I (1992) and Feat of Clay: Part II (1992) which also told the origin of Matt Hagen's Clayface.
Originally was meant to be in the DC Extended Universe and rumored to be part of Matt Reeves' The Batman Crime Saga but it was announced as part of the DC Universe.
Mike Flanagan couldn't direct the movie due to his commitments to his The Exorcist film and a Carrie miniseries.
Contains multiple north west UK filming locations. Notably NYL/Aloft building on north John street Liverpool and The Plaza in Stockport.