Avengers: Doomsday already has one of the most stacked casts of any superhero movie in recent memory. Marvel Studios has established that the movie will bring together the old and new Avengers, the Wakandans, the Fantastic Four, and the X-Men as they face off against the evil Doctor Doom. However, one industry insider claimed that Marvel hasn't revealed the movie's full lineup yet.
According to The Cosmic Circus' Alex Perez, some of the characters who will appear in Avengers: Doomsday won't be revealed until later in the film.
"The truth of the matter is there is a lot that isn’t really out there yet for Avengers: Doomsday regarding specific details, characters, or motivations," said Perez. "There are still some characters that are surprises for Doomsday, mainly around the third act."
When discussing any hidden characters, Perez speculated on why Marvel hasn't revealed whether Monica Rambeau will appear in Doomsday's cast.
"There’s no specific reason outside the possibility of wanting to keep some characters secret. And you’d think that even with all the plot leaks and everything people keep talking about, the cat’s out of the bag," said Perez.

The Marvels set up Monica's appearance in Avengers: Doomsday
Teyonah Parris's Monica Rambeau was last seen in The Marvels, which ended with her stranded in another universe after closing a multiversal rift. In the movie's post-credits scene, Monica meets a superpowered variant of her mother, Maria Rambeau/Binary, and the X-Men’s top scientist, Beast.
With this post-credits scene, the MCU featured the first big setup for the X-Men's appearance in Avengers: Doomsday. Since Beast is confirmed to return in Doomsday, it is possible that Monica will appear alongside him as well. Marvel is famous for its efforts to hide movie spoilers from the public, so it wouldn't be a surprise if the studio were going out of its way to hide Monica's role to avoid revealing a significant plot point in Avengers: Doomsday.

Monica Rambeau may have a major role in Avengers: Doomsday
If Monica does appear in Avengers: Doomsday, she could potentially serve as the link between the X-Men and the Avengers. The movie's marketing sets up members of the Avengers and X-Men fighting each other for some reason. Since Monica, who originated from the Avengers' universe, has already met a member of the X-Men, she could be the one who convinces them to stop fighting each other and to work together to stop their real threat.
It is also worth noting that Monica can close tears in spacetime, as shown in The Marvels. Since it seems like Doomsday will show the Multiverse on the brink of collapse from interdimensional incursions, she could be one of the few people who can stop this crisis from occurring.
Even if she doesn't appear in Doomsday, Perez suggested that she and Binary will play an important part in the story going forward. He stated that the duo will have more interactions that address Binary's quantum bands.
"If I had to take an educated guess based on the info I have heard, it would be that Monica and Maria are out and about together on a separate story while the events of Doomsday transpire. But I am confident that we’ll see both Teyonah Parris and Lashana Lynch return for one (if not both) Avengers outing."
At this point, it is unclear when Monica will return to the MCU. However, based on her character's journey throughout the Multiverse and the power she wields, she and Binary could play a significant role in saving all realities during or after Avengers: Doomsday.
