Robert Downey Jr and Pedro Pascal swap Avengers: Doomsday roles for Halloween

Robert Downey Jr and Pedro Pascal dressed up as each other's Marvel characters for Halloween, surprising fans just ahead of Avengers: Doomsday.

Downey, who will play Doctor Doom in the film, appeared as Reed Richards, the superhero known as Mr Fantastic in The Fantastic Four: First Steps. Pascal, who plays Richard, wore Doom's metal mask. The two actors are both part of the film's cast.

Downey shared a video of the costume swap on Instagram. He captioned it "Victor. Richard. Costume swap!" The post showed the two stepping into each other's roles.

Fans reacted with delight. One commenter wrote, "What universe are we in," while another joked about the multiverse. A third called it "the best thing ever."

Avengers: Doomsday brings together heroes from three separate universes. Anthony and Joe Russo are directing, and Kevin Feige, Louis D'Esposito and Jonathan Schwartz are producing.

The ensemble also includes Chris Evans, Chris Hemsworth, Paul Rudd, Anthony Mackie, Florence Pugh, Vanessa Kirby, Ebon Moss-Bachrach and Wyatt Russell.

It is not yet known when the film will be released. It is also not yet known whether the costume swap has any link to the movie's plot.