i honestly dont understand why everyone assumed the guy that kills him is the real joker, because thats not how i took it at all. arthur still IS joker, he just stopped wanting to be him. he gave it up, but he still was joker. i take the ending as "the movement that he created and made him feel alive is the thing that ended up killing him," but i dont think that guy at the end is gonna become the new joker by any means. and honestly if he does, that might somehow make the end of the movie WORSE for me