The sequel to Arthur Fleck’s story, Joker: Folie à Deux, is one big mystery. Viewers were initially surprised that pop icon Lady Gaga would play Dr. Harleen Quinzel, aka Harley Quinn. The singer admittedly already has quite an impressive acting career, but it probably never occurred to DC fans that she could star as the famous villain. Even more surprising was the news that Folie à Deux would be a jukebox musical. In various DC Comics adaptations, the Joker was a grotesque character, but the 2019 film offered a rather realistic and depressing look at the Clown Prince of Crime. Can the dark vib…