Avengers: Doomsday’s two biggest stars just gave Marvel fans the treat of the season — Robert Downey Jr. and Pedro Pascal traded Marvel characters for Halloween.

Downey — who plays Doctor Doom in the film — pulled on Reed Richards’ blue Fantastic Four suit, while Pascal — Mister Fantastic himself — went full Doom, complete with hood, cape, and silver mask.

Downey posted the reveal on Instagram on Oct. 31, captioned “Victor. Richard. Costume swap!” — and the video opens like a Doomsday teaser before the big reveal.

In a second clip, the pair stroll arm in arm through the streets on Halloween night. Downey even stopped to pose with young Star Wars fans, calling a kid in Mandalorian armor “the real Mandalorian.”

Eagle-eyed fans spotted Pascal’s Doom costume worn over an M.I.T. hoodie — sparking theories about a Reed/Doom connection in the movie.

Avengers: Doomsday opens in theaters December 18, 2026 — about six weeks away — with a cast topping 60, including Anthony Mackie, Letitia Wright, and Sebastian Stan.

Note: RDJ’s original Instagram post couldn’t be embedded natively at publish time, so we’ve linked to coverage of the video below.

Sources: Entertainment Weekly | Pop Culture Pit | ComicBook.com

Robert Downey Jr. at San Diego Comic-Con, Wikimedia Commons, CC BY 2.0.