My Wildest Avengers: Doomsday Theory Suggests One Of The Best X-Men Movies Will Be Required Viewing

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My biggest Avengers: Doomsday theory would make one of the best X-Men movies required viewing. Thanks to Marvel"s recent cast announcement livestream for Avengers: Doomsday, we know that multiple actors from Fox"s X-Men films will be appearing in the upcoming MCU crossover. However, I"m really hoping that we"ll be seeing even more as a means to truly close the door on Earth-10005 and Fox"s franchise.
Currently, there are seven X-Men actors confirmed to appear in Avengers: Doomsday. Additionally, the one thing they all have in common is that they"re all from the very first cast before Fox effectively rebooted their X-Men universe in 2011. However, my big Avengers: Doomsday theory suggests that we might very well see both casts, thanks to the MCU"s Multiverse Saga and its major stakes.
OG X-Men Actors in Avengers: Doomsday Is Genius (But It's A Half-Measure) There's A Whole Second Cast Of X-Men Actors Available

At present, we already know that seven actors from the OG X-Men franchise will be in Avengers: Doomsday. This includes Professor X (Patrick Stewart), Magneto (Ian McKellen), Cyclops (James Marsden), Mystique (Rebecca Romijn), Nightcrawler (Alan Cumming), Beast (Kelsey Grammer), and Gambit (Channing Tatum). As a side note, Tatum"s Gambit only sort of counts as an OG X-Men actor. While he only just made his live-action debut in 2024"s Deadpool & Wolverine, Tatum was considered to play Remy LeBeau and had been trying to get a Gambit movie made as far back as 2009.
Regardless, MCU fans are very excited to see so many X-Men characters join the Avengers to fight Robert Downey Jr. in a multiversal epic that will presumably be unlike anything we"ve seen before. However, Doomsday only having actors from the OG X-Men cast feels like a half-measure. Assuming more X-Men characters get added and are revealed in the future, my big hope is that members of the new cast will be involved, and there"s already a perfect narrative device Marvel could use to explain how, thanks to one of the X-Men franchise"s best movies.
Theory: Days of Future Past Can Explain The X-Men's Involvement In Avengers: Doomsday The X-Men's Alternate Future Could Have Had Multiversal Consequences... Close In 2014"s X-Men: Days of Future Past, Logan"s mind is sent back to his younger body in the 1970s from a dark future where mutant-killing robots known as Sentinels had nearly hunted all mutants to near extinction. The result was Wolverine interacting with the X-Men franchise"s younger cast, first introduced in 2011"s X-Men: First Class. While Logan and the younger versions of Charles Xavier (James McAvoy), Magneto (Michael Fassbender), Mystique (Jennifer Lawrence), Beast (Nicholas Hoult) and more worked to change the future, the original X-Men cast fought to protect Wolverine"s body, giving mutantkind a second chance to change their fate.
Days of the Future was incredibly exciting and successful for several reasons. Not only did it bring both casts together in the same movie with Hugh Jackman"s Wolverine as the bridge, but it also set the stage for a soft reboot for Fox where future movies could star the new cast in a brand-new timeline, as seen with future movies like X-Men: Apocalypse and Dark Phoenix. Likewise, Days of Future Past"s ending saw Wolverine waking up to a new present, one where his Cyclops and Jean Grey never died, as they did in 2006"s X-Men: The Last Stand.
Despite the positive results for both X-Men casts, Wolverine and company still massively changed and altered the timeline to a pretty egregious level. Based on the MCU"s own experience with time travel and the multiverse, one could easily imagine a scenario where Avengers: Doomsday reveals the unintended consequences for the Fox universe...like an incursion. The Avengers also messed with their own timeline in Avengers: Endgame, so perhaps both universes will be at risk of destruction in Doomsday ahead of Secret Wars, explaining why the teams of heroes will finally meet.
The Multiverse Saga Could Easily Bring Back The Old And New X-Men Casts Taking What Made Days of Future Past So Great (And Going Even Further)

Avengers: Doomsday has the opportunity to fully close the door on the Fox Universe ahead of the expected Mutant Saga and a brand-new cast of MCU X-Men. However, one could argue that it can only fully happen if the younger X-cast/timeline is also involved/referenced. While the younger cast doesn"t have to have full-on roles, it would be incredible if Days of Future Past and Logan"s critical alteration of the timeline is what leads to the universe"s ultimate incursion.
The Multiverse Saga could easily be used to incorporate the likes of James McAvoy"s Xavier or Fassbender"s Magneto just as much as Stewart and McKellen. If so, it would be cool to at least get nods and/or see a handful of faces from the younger X-Men cast just like we"re going to see from the OG cast like McAvoy, Fassbender, Tye Sheridan"s Cyclops alongside Marsden, or Evan Peters" Quicksilver (who"s already got MCU ties thanks to WandVision/Agatha All Along). While Days of Future Past had a moment where both Xaviers talked to each other via Wolveine"s mind, my dream is the Multiverse Saga going further with both X-Men casts fighting Doctor Doom side by side.
Avengers: Doomsday releases in theaters May 1st, 2026.

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