The decision to make “Folie à Deux” the project’s working title could mean a few different things. It could be a reference to the relationship Arthur Fleck (Phoenix) had with his mother Penny (Frances Conroy), who developed a severe mental disorder after being in an abusive relationship. What exactly she suffered from was unclear, and she was killed by her son before the audience could find out.

There is also the potential that young mother Sophie (Zazie Beetz) could somehow be involved in this sequel, given how Fleck was obsessed with her character to the point where he began having hallucinations of spending time together. Arguably the most controversial interpretation of the subtitle is that it will give viewers a new iteration of Harley Quinn. Despite Margot Robbie and Kaley Cuoco tag-teaming the role between live-action and animation, Phillips could be interested in bringing in his own version of the character.

Finally, in probably the most interesting interpretation, the “Joker” sequel might not even involve the first film at all. Remember, content like “The Killing Joke” comic arc and “The Dark Knight” emphasize that the Joker’s real identity and background will never be solved for as long as he lives. Perhaps “Folie à Deux” references a different, but somewhat similar or overlapping origin story for the Joker, a madness shared by two or possibly many, many others.