If Joker 2 happens, Arthur Flecks needs to fight Batman. In the wake of Joker’s staggering success at the box office, there has been talk of a sequel. At first, it appeared confirmed that director Todd Phillips would be returning for another go with the Clown Prince of Crime, but then Phillips dismissed those rumors as premature. Regardless, given Joker's critical and commercial success, Joker 2 would have a lot to live up to.
Joker is better equated to a character-driven indie than a big-budget blockbuster; Phillips and star, Joaquin Phoenix, approached the film with this in mind. The movie’s smaller budget is the main reason it is now considered the most profitable comic book movie of all-time. One of the reasons audiences are so drawn to its story is because of its ambiguous narrative - Arthur Fleck’s insanity serves as a blinder for the viewer. At many points in the film, neither the viewer nor Arthur are certain about what is real. Joker ends with Arthur in Arkham Asylum and leaves the audience wondering if the whole film was the delusion of a mentally disturbed man - laughing at a joke his psychiatrist “wouldn’t get”.
A major fan theory suggests that Arthur’s imagined the perfect backstory for himself (the Joker), one that directly ties his origin to his arch-nemesis (Batman) and paints him as a sympathetic character. Regardless, the intertwined plot possibility that Arthur is the illegitimate son of Thomas Wayne heightened the connection between the two iconic characters. All of the foreshadowing in Joker points to one thing about the sequel: if Arthur Fleck returns, he needs to fight Batman.
Joker Perfectly Set Up A Fight With Batman
The biggest moments of foreshadowing in Joker occur on two occasions. The first being the moment when Arthur meets a young Bruce Wayne at Wayne Manor and the second at the end of the film when Bruce’s parents are killed (in the canon way). The death of Thomas and Martha Wayne is inadvertently the fault of Arthur Fleck; it is Arthur’s “kill the rich” rebellion that caused all of the riots throughout Gotham and, therefore, the death of the Waynes. One can argue that Arthur does not intend to provoke an entire movement but he nevertheless does. The other pragmatic argument comes in the form of Joker’s timeline; Arthur is simply too old (in 1981) to fight an adult version of Bruce.
It's possible, then, that Arthur isn't the Joker at all, but that he merely inspires the real one. Similarly to Tim Burton’s Batman where Jack Napier kills Bruce’s parents and then becomes the Joker, the man at the end of Joker could do the same. This theory would not only be consistent with the many iterations of the character but the infamous quote from Alan Moore’s The Killing Joke: “If I’m to have past I prefer it be multiple choice.” The idea that the Joker can be anyone opens the door to a plethora of possibilities for Todd Phillips and even Joaquin Phoenix. What's more, when Bruce grows up, he would logically go after the Joker - instead of Joe Chill, who kills his parents in the comics - for being responsible for his parents' murders.
How Joker Could Fight Batman In The Sequel
There is a multitude of ways that Phoenix’s Joker could come into conflict with Batman. If Joker 2 chooses to explore the impact Arthur’s actions had on Gotham, then Batman could battle copycats (and would have a personal stake in it). Warner Bros could even decide to tie this version of the Joker into the DCEU as a symbol; Phoenix playing a completely different character (unbeknownst to everyone but the audience). Or, a sequel could explore the theory that Arthur’s origin story was all a fantasy and Batman already exists.
The aforementioned theory throws all of the timeline inconsistencies out the window. Arthur’s age does not matter if he was simply imagining himself in the 1980s; we do not know how much time has past at the end of the film. Joker 2 could pick up where the original left off, with Arthur escaping Arkham. However, this decision would take away a lot of Joker’s ambiguity and arguably tarnish the film. In order to leave as much of Joker intact as possible, Arthur would have to be a lot older when he comes in contact with the caped crusader. Whether or not Joker 2 happens is still up in the air; however if it does, then there needs to be a Batman, arguably at the expense of the first film.