Marvel fans are counting down to one of the biggest superhero events of 2026. Avengers: Doomsday is bringing together the Avengers, the Fantastic Four, and characters from the X-Men universe for a confrontation with Doctor Doom, played by Robert Downey Jr.

But the confirmed cast is only part of the excitement. Rumours about Loki’s fate, Spider-Man’s possible return, multiversal destruction, and Doctor Doom’s ultimate plan have fuelled countless fan theories.

With the movie scheduled to arrive in cinemas on December 18, 2026, here are the biggest Avengers: Doomsday rumours, what they could mean for the MCU, and which details remain unconfirmed.

1. Is Loki Going to Die in Avengers: Doomsday?

One of the most shocking rumours surrounding Avengers: Doomsday concerns Loki, played by Tom Hiddleston.

At the end of Loki Season 2, the God of Mischief sacrifices his freedom to hold the branching timelines together. His transformation makes him one of the most important characters in the multiverse storyline.

A later report attributed to online scooper James Mack claimed that Doctor Doom kills Loki during the film and that a post-credits scene could reveal Loki is still alive. The same report suggested that Loki might lose the extraordinary abilities he gained at the end of his series.

If this rumour proves accurate, Loki’s death could establish Doctor Doom as a threat capable of challenging even the most powerful characters in the MCU.

However, Marvel has not officially confirmed these alleged plot details. Fans should treat the story as speculation rather than a verified spoiler.

2. Will Spider-Man Return to Fight Doctor Doom?

Another major question is whether Tom Holland’s Spider-Man will appear in Avengers: Doomsday.

Spider-Man has become one of Marvel’s most popular heroes, and his experience with alternate realities in Spider-Man: No Way Home makes him a natural candidate for a multiverse-focused Avengers story.

Recent online rumours have suggested that Spider-Man could join the final battle against Doctor Doom. One circulating theory claims that Loki recruits heroes from different universes, potentially including Holland’s Spider-Man, for a last attempt to stop Doom.

The idea is exciting because Spider-Man could bring together the street-level storytelling of his solo films and the enormous stakes of the Avengers franchise.

However, Spider-Man’s appearance in Doomsday has not been officially confirmed. His potential involvement remains a fan theory, and Marvel could still have another plan for his next major crossover.

3. Doctor Doom Could Create Battleworld

Perhaps the biggest storyline rumour involves Battleworld, a setting associated with the famous Secret Wars comic-book storyline.

In Marvel Comics, Battleworld becomes a world formed from different realities under extraordinary circumstances. Doctor Doom plays a central role in the 2015 Secret Wars storyline, using immense power to rule over a reality assembled from fragments of destroyed universes.

This has led fans to speculate that the MCU’s Doctor Doom could manipulate incursions, events in which universes collide, to reshape reality according to his own vision.

Imagine the Avengers failing to prevent the destruction of their universe, only to awaken in a world controlled by Doom. Heroes from different realities might be forced to cooperate despite their conflicting histories.

Such a storyline would create a natural bridge between Avengers: Doomsday and Avengers: Secret Wars.

Nevertheless, Battleworld’s exact role in the film has not been officially confirmed. The theory draws on the comics and the movie’s multiverse premise, rather than a complete verified plot description.

4. Could the Avengers Fight the X-Men?

The confirmed cast includes several actors returning from Fox’s X-Men films, including Patrick Stewart, Ian McKellen, James Marsden, Rebecca Romijn, Alan Cumming, and Kelsey Grammer.

Their inclusion raises an important question: will the Avengers and X-Men immediately become allies, or could their different universes put them on opposing sides?

One popular fan theory suggests that the heroes might initially fight each other because of confusion surrounding the multiversal crisis. Doctor Doom could potentially exploit their disagreements before they realise that he represents the greater threat.

This would give Marvel an opportunity to recreate the tension of a major superhero crossover while introducing audiences to new relationships between characters.

It could also make the eventual alliance more meaningful, especially if the heroes have to overcome their mistrust before confronting Doom.

The cast is confirmed, but a specific Avengers-versus-X-Men battle has not been established as an official plot point.

5. Is Doctor Doom Connected to Tony Stark?

Robert Downey Jr.’s return to the MCU has created one of the most persistent fan theories surrounding Avengers: Doomsday.

Because Downey previously played Tony Stark, many viewers wonder whether Doctor Doom will be connected to Iron Man through an alternate identity, a variant, or some other multiversal twist.

The resemblance could create an emotional challenge for the Avengers. Imagine Steve Rogers or Thor facing a villain whose appearance reminds them of their former friend.

However, Marvel’s official information identifies Downey’s new role as Victor von Doom. A direct connection between this Doctor Doom and Tony Stark has not been confirmed.

The casting creates interesting dramatic possibilities, but it does not prove that Doom is an evil version of Iron Man.

6. Will Avengers: Doomsday End With a Major Cliffhanger?

Another widely discussed possibility is that Avengers: Doomsday will end without a traditional victory for the heroes.

The film could leave the multiverse in danger, separate familiar characters into different realities, or establish circumstances that lead directly into Avengers: Secret Wars.

This approach would follow the structure of a larger two-film storyline, allowing the first movie to establish Doom’s threat while reserving the ultimate resolution for the sequel.

A cliffhanger could also explain why characters from multiple universes are needed for the next chapter.

However, the exact ending remains unconfirmed. Predictions about deaths, sacrifices, and the destruction of particular universes should not be mistaken for verified spoilers.

Final Verdict: Which Avengers: Doomsday Rumours Should You Believe?

The biggest Avengers: Doomsday rumours involve Loki’s possible death, Spider-Man’s potential return, Doctor Doom creating Battleworld, and a possible conflict between the Avengers and X-Men.

These theories are compelling because they connect the film to established Marvel stories and the wider multiverse storyline. However, the existence of a convincing theory does not make it true.

For now, the safest approach is to separate official announcements from unverified reports. The confirmed cast and multiverse premise provide plenty of reasons for excitement without relying on alleged leaks.

With Doctor Doom emerging as the MCU’s next major villain, Avengers: Doomsday could change the future of Marvel’s cinematic universe. The biggest mystery is whether the heroes can stop him before their realities collapse.

Whatever happens, the answers could set the stage for Avengers: Secret Wars and the next era of Marvel storytelling.