Why The X-Men Are In Avengers: Doomsday, And How Monica Rambeau Could Trigger The Incursion

The original Fox X-Men actors confirmed for Avengers: Doomsday are there because their universe is on course to crash into the MCU's Earth 616, a cosmic event known as an incursion. As of April 2025, my theory was that Monica Rambeau's arrival in their world at the end of The Marvels is what sets that collision in motion, and that the X-Men, especially Beast, will be the ones scrambling to stop it.

When Marvel Studios revealed the Doomsday cast with a long line of chairs, many people outside the comic reading audience were left wondering what purpose these X-Men would serve and why the plot needs them. My answer is that their inclusion is set to cause some huge problems for the heroes of 616.

The Fox X-Men universe is heading for an incursion with Earth 616

Alongside the MCU names, Marvel Studios officially revealed that the actors who played Beast, Nightcrawler, Cyclops, Mystique, Magneto and Professor Charles Xavier in the original Fox X-Men trilogy would be involved in the multiversal mayhem. The main reason actors from a completely separate cinematic universe are joining the MCU's next big event is that their X-Men universe is essentially going to crash into Earth 616.

Marvel Studios has teased incursions ever since Doctor Strange got a surprise lecture in Doctor Strange in the Multiverse of Madness. The Reed Richards of Earth 838 warns him that because he and America Chavez are beings from another universe who were not supposed to exist in 838, their presence risks Strange's native universe crashing onto the doorstep of the Illuminati's Earth. As Reed puts it: "Stephen, your arrival here confuses and destabilizes reality. The larger the footprint you leave behind, the greater the risk of an incursion."

That is the main reason the Illuminati rushed to shove Strange and America into those near indestructible glass holding cells as soon as they arrived. As we learned in depth across both seasons of Loki, the flow of time is inextricably linked to the choices of living souls. As an aside, that is why I believe the TVA is modelled on green and orange, the colours of the Time Stone and another of the stones. Had the Illuminati not contained them, a tiny branch of Strange's 616 timeline would have started growing wildly into the 838 timeline, and the 616 universe would have started showing up unannounced.

Multiverse of Madness showed what happens when the walls between universes break down

We got a brief glimpse of a broken reality after Wanda Maximoff throws 616 Doctor Strange and 838 Christine Palmer into a dying universe that has suffered an incursion. As the two walk around that Earth, they are surrounded by gravitational anomalies: floating buildings, cars, benches and bridges, random tornadoes, and everything touching the ground disintegrating and drifting into the sky.

The same thing happens to the Sanctum of Sinister Strange when 616 Strange visits. In the background of their conversation sits the biggest anomaly of all, a huge cloudy tunnel of debris that the Sanctum is slowly dissolving into. I believe that tunnel leads to the universe that had a catastrophic incursion with Sinister Strange's universe.

My reasoning comes from how gravity works in science. Objects with larger masses have stronger gravitational pulls. That is why our planet tugs the Moon around us every day and why the Sun keeps the entire solar system of planets dancing around it. Gravity is a core aspect of every universe that holds everything together, and it even dictates the flow of time depending on the mass of the object you are sitting on. "It's pretty wild stuff." So what happens if the fabric of reality starts tearing itself apart and opens gravitational wormhole portals to alternate versions of Earth? Another massive Earth in the sky would cause a huge amount of gravitational disturbance as the two planets pull against each other.

The Marvels already tore a hole toward the X-Men universe

If that is hard to picture, this is pretty much why Marvel Studios made the underrated and super fun The Marvels in 2023. The Kree warlord villain Dar-Benn used the power of her Quantum Band to tear holes in reality and open portals to her dying home planet of Hala, then used Hala's gravity to pull resources from other planets, as we see her do to the planet Aladna.

At the end of the film, Dar-Benn tries to tear another hole above Earth so Hala's gravity can drain Earth's Sun as well. But she overloads herself with too much cosmic power near the tear she created, and the resulting explosion opens a rapidly expanding fault in reality that pulls the 616 timeline over toward the neighbouring X-Men universe timeline.

That is technically where the events of Avengers: Doomsday could have started, were it not for the brave and selfless sacrifice of Monica Rambeau. After being charged up with energy from both Captain Marvel and Ms. Marvel, she uses her powers to close the tear in spacetime. But patching that particular hole did not solve the whole problem. In my view it only delayed the inevitable, and it might have made everything considerably worse.

Monica Rambeau's presence could be what breaks the X-Men universe

It was really cool to see Kelsey Grammer back as Beast, checking Monica's vital signs after she fell onto their planet, and equally wild to see Maria Rambeau as the hero Binary in that universe. But I believe Monica interacting with these mutant heroes is exactly what will cause the conflict between her and their universe.

The heroes of this X-Men universe are clearly not doing what the Illuminati of Earth 838 did. For whatever reason, they do not seem to have had the foresight to put Monica in a glass prison, and they could not prune her out of their timeline with a TVA pruning stick because they do not have that technology. So Monica's very presence is slowly weakening the walls of that reality, which will eventually cause those walls to break down entirely. That is exactly what she was trying to avoid.

This also fits a Doomsday rumour from The Cosmic Circus, which stated that Monica will apparently have a role similar to Vision's in Avengers: Infinity War. I believe that means the war between universes will start because of Monica, much like the Infinity War was brought to Wakanda because of Vision. In my view, it will be Monica who essentially triggers the events of the film.

Beast could be the first to realise Monica's presence means an incursion

This is where the X-Men come in, especially Kelsey Grammer's Beast, who I believe will play a massively important role thanks to his extraordinary intelligence. He is one of the most knowledgeable people on the planet in human biochemistry and genetics, and he knows how to build incredibly complex science fiction machines, including the X-Jet.

Because we saw Beast analysing Monica and her life signs at the end of The Marvels, I am assuming he will be one of the first people in that universe to realise her presence will eventually cause an incursion. That is, unless the Professor Xavier of that universe is part of his own secret Illuminati group, as 838 Xavier was. If he is, I am sure Xavier will be the first to instruct Beast to find a way to get Monica back to her universe immediately. Either way, I think Beast's main role will likely be trying to prevent Doomsday entirely by sending Monica back to Universe 616.

Xavier and Nightcrawler could team up to send Monica home

This is where I believe Patrick Stewart's Charles Xavier and Alan Cumming's Nightcrawler could come in majorly handy, working in tandem with Beast. When Cumming debuted as Nightcrawler in X2: X-Men United, we learned that to teleport somewhere safely he typically has to have been there or have the destination in sight or in mind. Even then, he is typically limited in how far he can go.

If Professor Xavier used his powers to project Monica's memories of Earth 616 into Nightcrawler's mind, I believe there is a chance Nightcrawler could use that imagery to lock onto the 616 dimension and teleport her home. He would not manage it alone, of course, so he would very likely need a machine to amplify how far he can teleport, one that Beast could theoretically build.

I only bring this up because we saw something similar in 2015's Secret Wars #1. In that issue, the Illuminati built a machine that amplified the powers of another teleporting mutant, Manifold, and used it to bring the heroes they needed to an ark they had designed to survive the destruction of the multiverse. I can see Marvel using that issue as inspiration, swapping Manifold for Nightcrawler to send Monica home. "But that's just a wild theory based on those elements."

A different universe's Illuminati, possibly with Doctor Doom, could turn on Earth 616

We also have to consider the strong possibility that Beast and or Xavier will be part of their universe's own Illuminati, possibly alongside Robert Downey Jr.'s Doctor Doom. Another universe's Illuminati coming to battle Earth 616 was teased at the end of Captain America: Brave New World, where Samuel Sterns tells Sam Wilson that other worlds protected by other superheroes exist in the multiverse and that he foresees an unstoppable incursion threat on the horizon. Director Julius Onah has confirmed that scene refers specifically to another universe's Illuminati arriving in Avengers: Doomsday.

In the comics, both Xavier and Beast have been members of the Illuminati, with Beast taking Xavier's place on the secretive team after Xavier's apparent death at the time. So I think it is very likely one or both will be part of this team organising a defence against a possible invasion from 616, and that Monica will be brought before their council for questioning and consultation, since she is insanely smart about the cosmic scene too. To be clear, this would be a completely different Illuminati from the one in 838. The implication seems to be that most universes with heroes have an Illuminati type team prepared for multiversal visits, especially if they had the events of Avengers: Endgame in their past. That also makes it likely Maria Rambeau's Binary is involved, much like 838's Captain Marvel was.

Because the Illuminati is typically made up of the smartest and most influential minds on the planet, Doom's inclusion would also be highly likely. Even though he is typically a villain with selfish motivations, he is not so evil that he would refuse a temporary alliance with other geniuses to stave off the apocalypse. I imagine that once Monica explained her arrival, Xavier likely brought her to the Illuminati himself, wanting to send her back as soon as possible to prevent the loss of life that comes with a multiversal war of heroes.

The mutants could split, while Xavier and Beast build an ark

When the incursion seems all but inevitable and the walls start breaking down, I think drastic minds like Doom will seek to attack 616 to preserve their reality rather than pursue peace and understanding. He could recruit enhanced people who share that view from both Xavier's X-Men and Magneto and Mystique's Brotherhood of Evil Mutants.

There was also a recent rumour that Famke Janssen had signed on to return as Jean Grey for the first time since Days of Future Past. If so, it would be super interesting to see a rift form between Cyclops and Jean in this scenario, with Cyclops wanting to join Doom in defending the planet while Jean sides with the Professor in searching for nonviolent solutions.

I could also see Xavier, Beast, Monica and the more peaceful members of the Illuminati eventually working on an ark to survive the end of everything, as the Illuminati did in Secret Wars #1. They would likely work alongside the big brains of Earth 616: Black Panther, Smart Hulk, the Pym family, maybe even Spider-Man, Rocket Raccoon, Vision, and possibly even the Fantastic Four. That is why I believe the X-Men are in Avengers: Doomsday and what I think they will be up to.

Do you think Monica Rambeau is really the spark for the incursion, and would you side with Xavier's peaceful plan or Doom's attack on 616?