It’s essentially a Joker sequel, picking up from Joaquin Phoenix’s 2019 movie, but also bringing in the late Heath Ledger’s Joker from The Dark Knight and Jared Leto’s Joker from Suicide Squad — plus Ben Affleck’s Batman, Margot Robbie’s Harley Quinn, Amy Adams’ Lois Lane, and even Jack Nicholson!
Not in full Joker makeup from the 1989 Batman movie, but billed as “Joe Chill” in the YouTube credits, for the Gotham City mugger who killed Bruce Wayne’s parents.