well, other than the fact that he's a huge piece of shit and probably a terrible actor... but on a purely physical level? I've never seen a person who looked more like the comic book Joker in my entire life
(I don't actually want this to happen I'm just saying)
Joker III should just have a title card that says
spoiler
Joker died in the last movie
and then the entire movie is about Harley and Poison Ivy going on dates where they do ecoterrorism and build a mountain.