Ever since Disney acquired 20th Century Fox – and with them the rights to wayward characters like the X-Men and the Fantastic Four – the question has lingered about how Marvel’s mutants might enter the Marvel Cinematic Universe. Unlike the Fantastic Four, whose previous onscreen appearances were limited and largely regarded as failures, the X-Men have a lengthy and, at times, celebrated legacy to live up to. While the Fantastic Four are all but assured to arrive in Phase 4, the X-Men’s arrival is almost entirely an unknown. Beyond the fact that they will eventually appear in the MCU, fans have little else to go on.
One Reddit fan theory believes it has discovered a clue. A line in the middle of Avengers: Endgame – barely audible in theaters, but readable in onscreen subtitles – suggests a link to Marvel’s Merry Mutants. It even name-drops one and strongly hints at another. If the theory holds true, there won’t be any waiting for mutants in the MCU. They’re already here.
There is certainly no shortage of cosmic-level events on the record to facilitate the rise in mutants. People restored by the Blip, for instance, could come back with altered DNA, in which case their children might start exhibiting mutations once they hit puberty. (Perhaps 15-20 years of in-world time.) Or they could conceivably arrive from different realities in a manner similar to that seen recently in Spider-Man: No Way Home. Whatever the justification, it’s bound to cause a splash when the MCU reveals its intentions.
A Reddit theory posted in 2020 posits a very different explanation. It centers on dialogue between Peggy Carter and an unnamed aide during a key sequence of Avengers: Endgame. Having failed to secure the Tesseract after time-traveling to the Battle of New York, Tony and Steve use their remaining Pym Particles to travel back to 1970, where they hope to gain both the Tesseract and more Particles to return to the present. In the middle of it all, Steve inadvertently eavesdrops on Peggy, which presumably helps fuel his ultimate decision to remain in the past with her after returning the Stones at the conclusion of Endgame.
Amid the emotional sweep of their still unrequited feelings, the dialogue itself is easy to miss: deliberately downplayed to focus on Steve and his emotions. Carter appears to be handling some kind of paranormal incursion, but the details feel very familiar to Marvel fans. The dialogue mentions someone named Braddock being halted by lightning strikes. When the unnamed aide offers to check the weather projections, Carter responds that lightning might not be what they’re looking at.
Mention of the name “Braddock” immediately evokes Captain Britain, a figure who has not yet been seen in the MCU, but who has close ties with the X-Men. It might also refer to Psylocke, a long-standing team member who – if the theory is to be followed – is actually working for SHIELD in 1970. Coincidentally, the scene’s 1970 date falls within the timeline of the X-Men movies, more specifically between the events of X-Men: First Class and X-Men: Days of Future Past. Both movies entailed events set before and during Vietnam, so the presence of mutant activity in that era would have some onscreen precedent.
But the real tip-off, of course, is the mention of the lightning strikes, and how they might not be the result of random weather. While it could signal any kind of strange phenomenon, it bears all the hallmarks of Ororo Munroe, signaling that she and perhaps other X-Men are active during that time. Not only would it fit the historical events depicted in earlier X-Men movies, but it would roughly match the characters’ famous rebirth in 1975’s Giant-Size X-Men #1. Such a move would be surprising, but it could fit what the MCU has in mind for mutants quite well. It would even connect their creation to the events of Endgame, just not the part that fans might think.