Until Avengers: Doomsday debuts—or until screeners go out—the rumor mill will remain consistently flowing. Recently, several new ones have made their way online, and they have all the elements of a fan-fueled film. Robert Downey Jr., for instance, is in the movie in more than one role.

Fans are aware that RDJ is set to portray Victor Von Doom in the aptly titled Doomsday, but what fans don't know is that he'll also make an appearance as Iron Man. Mind you, this isn't a sign of a resurrection happening.
In all likelihood, Downey Jr. will be in a flashback related to Avengers: Endgame or the aftermath that was never shown in the theatrical cut. Fans have all kinds of theories about how Tony Stark survived—simply because there was no corpse at the end. Of course, an open-casket funeral wouldn't be possible since Stark became one with his armor.
To explain a little better. The radiation emitted by the Infinity Gauntlet caused an eruption of energy to flow throughout Tony Stark's body. The resulting heat burned the suit onto him since he was only a human; pieces of the armor were still smoldering as Rhodey checked Stark's vitals.

By the time everyone said their goodbyes, the suit would've been grafted onto Tony's body; explaining why his funeral only included floating a reef carrying Stark's arc reactor onto a river, but not a traditional casket and ceremony.
Captain Hydra
Another rumor floating around is that Chris Evans will rejoin the MCU as a variant of his former character: Captain Hydra. Just like the name sounds, Evans might be playing a brainwashed version of Steve Rogers, one who becomes a sleeper agent until Hydra makes its move for global domination. Such a move would be the biggest departure from Rogers' Captain America, though not surprising.
One of the fractured images teased on Marvel's What If showed a Captain America variant with a green cowl, teasing the arrival of an animated Captain Hydra. With that in mind, a live-action version could potentially enter the fray.
Unfortunately, much like the RDJ rumor, the Chris Evans return is unlikely. The actor has refuted such claims, stating that he's retired from playing Steve Rogers. He may change his mind, but for now, Captain America is out.
Rebranded Scarlet Witch

There is one rumor going around that has evidence to it: Elizabeth Olsen returning as Scarlet Witch. Marvel Studios quietly announced plans to bring the Wandavision star back to the MCU, though hardly anyone paid attention. Further proof lies in the Disney Plus series, Agatha All Along.
The show featured Billy Maximoff on a journey to become Wiccan. By the end, Billy ventured off to find his brother's wandering soul. Tommy isn't in the MCU yet, but he should be soon. And when he returns, a Maximoff reunion is the likeliest outcome.
Avengers: Doomsday opens in theaters on May 1, 2026.