'Joker: Folie à Deux' trailer shows Lady Gaga in action as Harley Quinn

The teaser trailer for "Joker: Folie à Deux" features Joaquin Phoenix as Arthur Dent, a patient at Arkham State Hospital, and Lady Gaga as Harley Quinn. The trailer hints at their tumultuous relationship and their descent into madness. The film, set to release on October 14, promises a gripping continuation of the supervillain's story.