The
Doomsday subtitle, the return of the Russo brothers, and the casting of Downey as Doctor Doom were all announced at Marvel Studios' SDCC panel in July 2024. The announcement involved multiple people dressed as Doom appearing on stage, including Downey, who unmasked himself to reveal his casting to the audience. Kat Bailey at
IGN described the casting announcement as "one of the most dramatic reveals in recent Marvel history" and reported on mixed responses from fans, with some praising Downey's return while others thought it was a desperate move from Marvel Studios following the creative reshuffling caused by Majors's firing. Other commentators also discussed the casting and mixed responses to it, including
Collider Collier Jennings who criticized the casting of a non-
Romani actor considering the character's comic book heritage. Coinciding with the start of production in March 2025, Marvel aired a nearly five-and-a-half-hour-long
livestream showing a line of
director's chairs with cast member names on them. A new chair was revealed approximately every 12 minutes, accompanied by music from a relevant previous Marvel project. After revealing 26 cast members, the livestream ended with an appearance by Downey and a rendition of Silvestri's
Avengers theme. The livestream saw around 100,000 concurrent viewers on
YouTube, and an hour-over-hour audience growth, to become the most viewed cross-platform livestream stunt. It became the second-most trending video on YouTube with 275 million views in its first 24 hours, surpassing past livestreams for Marvel's
red carpet premieres. The livestream also accumulated 3.1 million mentions across social media, which is five times higher than the "social volume" of the first trailer for
Deadpool & Wolverine. It garnered 55 distinct trending terms on
X (formerly Twitter) and the
hashtag "AvengersDoomsday" was the top trending topic on the site for over seven hours. Numerous
Internet memes were generated with each cast announcement. Anthony D'Alessandro of
Deadline Hollywood described the stunt as a "pop cultural event".
Variety Jordan Moreau and Brent Lang called the livestream a "slow-burn" and likened it to the release date reveal for the
seventh season of
Game of Thrones in 2017, which saw a block of ice melt to reveal the date; both stunts were "mocked for their pace". Austen Goslin of
Polygon, who was concerned about the large size of the announced cast, described the livestream as "agonizingly slow [but] exceedingly fun". He enjoyed checking the stream for each new reveal and seeing responses on social media. James Whitbrook of
Gizmodo said the livestream's viewership spoke to Marvel's "ability to maintain much of that grip it's had on pop culture over the past almost 20 years". The Russo brothers and
Scott Lang / Ant-Man star
Paul Rudd introduced footage from the film at
Destination D23 in August 2025. Disney's Merchandise Expo in China the following month featured concept art of Doom from the film; a light show centered on Doom, featuring logos for the Avengers, X-Men, and Fantastic Four; and a recreation of a panel from the 2015
Secret Wars comic series in which Doom rips the skeleton out of
Thanos's body. In December,
Doomsday was featured at Disney's Giornate Di Cinema Sorrento presentation in Italy. The announced cast was grouped by their teams: the Fantastic Four; the X-Men; the New Avengers;
Sam Wilson / Captain America's "Heroic Avengers" team, which included
Thor,
Xu Shang-Chi,
Joaquin Torres / Falcon, Ant-Man, and
Loki; and the "Wakandan Warriors", which included
Shuri / Black Panther,
M'Baku, and
Namor. On December 18, 2025, the Russo brothers released a short teaser of a 12-month countdown clock to mark a year until the film's scheduled release. Different short teasers were shown during each of the first four weeks of screenings for the Disney film
Avatar: Fire and Ash, starting with its release on December 19: the first revealed the return of Evans as Rogers and shows him holding a baby; the second features Thor praying to his father
Odin for the strength to return to his adopted daughter
Love after the coming battle; the third focuses on the X-Men characters
Charles Xavier / Professor X,
Erik Lehnsherr / Magneto, and
Scott Summers / Cyclops, and shows a ruined
Xavier's School for Gifted Youngsters; and the fourth is centered on the Wakandans and
Talokanil, with Shuri and M'Baku meeting the Fantastic Four member
Ben Grimm / The Thing. The teasers were released online on December 23, December 30, January 6, and January 13, respectively. Each teaser ends with the countdown clock. They were all noted for their similar "serious and somber" tone, and for a focus on children, continuing from the post-credits scene of the film
The Fantastic Four: First Steps (2025) which focuses on
Franklin Richards. Jesse Schedeen at
IGN appreciated the return to a more serious tone for Thor following the more comedic approach taken under director
Taika Waititi with the films
Thor: Ragnarok (2017) and
Thor: Love and Thunder (2022).
Gizmodo James Whitbrook enjoyed the first look at a Fantastic Four member interacting with other MCU characters in the fourth teaser, which includes characters that debuted in, or are closely associated with, the
Fantastic Four comic books. Doom's absence from the teasers was noted by commentators, with Marco Vito Oddo at
ComicBook.com calling it a smart move to build anticipation for the character. He believed Doom would be revealed in a full trailer targeted at a global audience. All four teasers were leaked ahead of their online releases. Germain Lussier at
Gizmodo expressed frustration with the rollout, feeling it was fumbled by Marvel due to the leaks. He was underwhelmed by the initial countdown teaser that was released after news of the Evans teaser already leaked, said the leaks undermined the studio's plans to get a "big, exciting, in-theater [fan] reaction" to Evans's return, and added that Marvel fans were "not used to major news being confirmed via bootlegged clips, wrapped in uncertainty of where and how to see things".
The Hollywood Reporter Borys Kit and Aaron Couch described the teaser approach as a "unique rollout" that was attempting to get "diehard" Marvel fans to see
Fire and Ash multiple times in theaters. Jeremy Mathai at
/Film also described the rollout as unique and said it had driven online discussion, but some of this was about how "un-hyped" some were feeling about the sombre teasers. After the X-Men teaser was released,
ComicBook.com Chris Agar said it was the best so far and there was an escalation from showing Rogers at peace, to Thor preparing for battle, to Cyclops "firing an optic blast into the sky in rage". Kyle Anderson of
Nerdist also believed there was an increase in quality and excitement with each of the four teasers, and
/Film Sandy Schaefer said the Wakanda teaser was Marvel saving the best for last. Whitbrook felt the fourth teaser was "muted" compared to the previous three and their focus on "familiar heavy hitters". Schedeen believed the focus on past lead actors over new characters who were introduced since
Endgame indicated that Marvel was pivoting to reinvigorate casual fans who "checked out of the MCU once Evans and Downey did". The four teasers collectively accumulated 1.02 billion online views within three days of the fourth being released. Couch said this was a "massive sum" considering they were not tied to a promotional broadcast. Together the teasers had more views than any single Marvel trailer on
Instagram (505 million) and
TikTok (103 million), each teaser had on average a 188 percent higher "social volume" than most Marvel trailers, and the rollout generated 16 distinct trending terms on X. Couch said Marvel was aware the teasers would leak once they were in theaters, and the studio saw the rollout approach—which required collaboration with theaters around the world—as a continuation of the cast reveal livestream. Based on the viewership, Couch believed the leaks had not impacted fan enthusiasm and said "the experiment paid off in a big way". The Russo brothers said the teasers each gave narrative information, and described them as "stories" and "clues" rather than teasers or trailers. Despite responding negatively to the teaser rollout and the Russos' "cryptic" comments, Lussier conceded that the approach was working since people were talking about the film 11 months before its release. There was speculation about whether Marvel continued practices from previous films of using footage shot specifically for marketing, or altering footage to hide certain characters or details. Anderson believed the Wakanda teaser was the only one of the four to feature actual scenes from
Doomsday. That teaser debuted online through a livestream on Marvel's YouTube account that transitioned to be a livestream of the countdown clock, continuing the "tradition" established with the cast reveal livestream. Commentators questioned whether the countdown livestream would be used to reveal additional information about the film leading up to its release. Lussier felt the livestream was unnecessary since the countdown was included at the end of each teaser. Feige, Downey, Evans, and the Russos promoted the film at
CinemaCon in April 2026 and showed a full trailer to attendees. It features narration from Doom, warning of an imminent multiversal threat, and Thor; Rogers wielding
Mjolnir; and numerous character crossover interactions. Commentators noted that the trailer finally revealed Downey's Doom. Lisa Richwine for
Reuters said the trailer was well received by the audience, prompting Downey to request it be played again. In a list of CinemaCon winners and losers,
The Hollywood Reporter James Hibberd listed Marvel as a winner. He also reported on the positive response from attendees, including some who said they had "never experienced a response that overwhelming" at the convention, and said the decision to show the trailer twice was "a move brimming with
BDE". == Release ==