Todd Phillips' film is one of the most highly anticipated of the festival, playing in the official competition five years after "Joker" won the Golden Lion. Warner Bros. is giving the dark comic book film the glitzy festival treatment before it's released in theaters in October.
"Joker: Folie à Deux" finds' Phoenix's Arthur Fleck institutionalized at Arkham and awaiting trial for his crimes. There he meets Gaga's Harley Quinn.
"We knew we had to swing for the fences; we wanted to create something as crazy and fearless as Joker himself," Phillips wrote in his directors' statement. "So, Scott Silver and I wrote a script that delved further into the idea of identity. Who is Arthur Fleck? And where does the music inside him come from?"
The Joker sequel is competing for the festival's main prizes against the likes of Pedro Almodóvar's "The Room Next Door," Luca Guadagnino's "Queer," Pablo Larraín's "Maria" and Halina Reijn's "Babygirl." Awards will be presented on the final day of the festival, Sept. 7.
In a lineup full of major Hollywood stars, including the likes of Angelina Jolie, George Clooney and Brad Pitt, there is also quite a bit of excitement about what Gaga might wear.
Six years ago, for "A Star Is Born," she played the part of movie star perfectly, with grand looks and entrances that gave the festival some of its most iconic shots this century. Remember her perched on the side of the private water taxi in that black Jonathan Simkhai bustier dress, blowing kisses to fans and photographers? Later, for the red carpet, she wore a show-stopping pale pink feathered Valentino Couture gown that seemed to pop even more against the rainy backdrop.