Farrell, who portrays Oswald 'Oz' Cobblepot, a.k.a. the Penguin, in The Batman (2022) and the HBO series The Penguin (2024), was surprised to learn that his character was originally intended to appear in Robbie’s Birds of Prey film. As Farrell explained that their characters:

Margot Robbie says The Penguin was the original villain of "Birds of Prey" before "Batman" filmmaker Matt Reeves asked her to change that.