While Calendar Man was once an incredibly gimmicky villain who was best known for committing crimes on the holidays, he turned a corner and developed into a thrilling character during celebrated Batman story, The Long Halloween. The arc sees him clearly modelled after Hannibal Lecter, helping Batman sort out clues to the identity of a killer while he languishes behind bars. Theres no reason that this exact same approach to the villain couldnt be taken to film. He may not have the physical presence to be a main antagonist but his cerebral prowess would allow the film to focus on Batmans detective side. The Joker has long been able to exert his influence even from prison that same quality could easily be afforded to Calendar Man, albeit in a more though-out manner. If the film is more blockbuster than mystery, Calendar Man may not have a place, but looking at Ben Afflecks filmography suggests this may be a darker interpretation of the character, making him a perfect choice for inclusion.