If there is any comic book team that has had more essential crossovers than any other, it has to be that of the X-Men. The X-Men have participated in numerous crossover events that have shaken up the world, changed their universe more than once, featured several other superhero teams, and created almost unlimited alternate realities. The original crossover events often emerged unexpectedly and shook up the entire mutant world, forcing readers to piece together what had happened along the way. That has happened again with the 2025 crossover X-Men: Age of Revelation, which, similar to Age of Apocalypse, has the X-Men in a strange world where nothing is as it was before.
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From worlds where Sentinels take over to a universe where Apocalyptic becomes the ruler and one where the entire Marvel Universe is destroyed, here is a look at the mutant crossover events that changed the world.
10) Age of Revelation (2025)
It remains to be seen if X-Men: Age of Revelation becomes as notable as other X-Men mutant crossover events. The new 2025 event series opened with a world where the mutants are the ruling class. It all started with a disease that began to kill non-mutants in Philadelphia, and those who lived became mutants. While the mutants tried to live peacefully in Philadelphia, the United States wouldn’t accept this and tried to launch a nuclear attack, one that was diverted back to Washington, D.C., and the U.S.A. never recovered. It turns out that the mastermind was none other than Douglas Ramsay, the mutant that Apocalypse renamed Revelation, who now possesses the power to compel people to comply through the power of his voice. It is up to Cyclops and other survivors to go back in time to prevent this future from happening. X-Men: Age of Revelation will cover 16 different Marvel Comics titles.
9) X-Cutioner’s Song (1992)
X-Cutioners Song is a 1992 X-Men event series that crossed over with X-Men, Uncanny X-Men, X-Factor, and X-Force. This opens with what appears to be X-Force leader Cable attempting to assassinate Professor X, and shortly after, the Horsemen of Apocalypse launch an attack on the X-Men. This leads to X-Factor and X-Men attacking X-Force as they attempt to locate and apprehend Cable. Mister Sinister is also involved, as he tries to distract the mutants with a war against Apocalypse. The assassin, however, is not Cable. It is his clone, Stryfe, and his Mutant Liberation Front. This introduced Stryfe to the Marvel Universe, and it changed every mutant’s life when the X-Men crossover series unleashed the Legacy Virus into the world, which killed countless mutants over the following years before a cure was found.
8) Onslaught (1996)
When it comes to X-Men mutant crossover series changing the world, nothing did it on a grander scale than Onslaught. Named after the villain, Onslaught was created after Professor X shut down Magneto’s mind when he realized that the mutant terrorist would never stop. However, the result was Magneto’s evil essence transferring into Xavier. This created a new being called Onslaught, which combined the powers of the two mutants. He was so powerful that it took the entire Marvel Universe to stand up and fight him, and it still wasn’t enough. Every hero in the Marvel Universe died, and the whole universe exploded. This led to Heroes Reborn, which rebooted every hero’s series. However, this was all undone when it was revealed that Franklin Richards had created the pocket universe in which this reboot took place. After Onslaught was finally gone, he rebuilt the original Marvel Universe.
7) Inferno (1988)
The Inferno crossover series took place in 1988 and was the result of Mister Sinister’s machinations and Cyclops’ selfish actions. After Jean Grey died, Cyclops resigned from the X-Men and went to live in Alaska in peace. He met a new woman who looked exactly like Jean, named Madelyne Pryor, and the two got married, having a baby named Nathan. However, when Scott learned Jean was alive, he left Madelyne and his baby. Mister Sinister abducted the baby and attempted to kill Madelyne, which led to her transformation into the evil Goblin Queen, blaming Scott for everything. Inferno then splits into the New Mutants battling the demon S’ym for Magik’s soul and the X-Men battling the Goblin Queen as she literally brought hell to Earth. This was the very first X-Men crossover series that spanned various titles, and while it isn’t as good as later stories, it primarily reset the original status quo of the pre-Madelyne X-Men world.
6) House of M (2005)
House of M is a Marvel-wide crossover event in which the entire world was changed in an instant, and only one person knew something was amiss. The story started in a confusing manner, similar to the best mutant crossover events. At the start, the Avengers and X-Men decide that they need to kill Wanda to prevent her from destroying the world after Avengers Disassembled. However, before they can do it, the world changes and everyone is living their best lives, including the mutants, who are no longer feared. Only Wolverine knows something is wrong and realizes that Wanda’s magic created a dystopian world, and he sets out to bring things back to normal. The ending of this crossover series changed the entire mutant world when Wanda realized what happened and said “No More Mutants,” stripping all but under 200 mutants of their powers.
5) X of Swords (2020)
X of Swords is a Krakoa-era crossover event that basically amounts to the mutant world’s version of Contest of Champions. Arakko is Krakoa’s twin sister, and both became the homes of mutants during that time. However, unlike Krakoa, where mutants lived in peace, Arakko was a violent place that lived and died by the survival of the fittest. When a gate was opened between the two worlds, the mutants of Arakko decided they wanted Krakoa for themselves, and a battle was presented with 10 mutants from each world set to battle each other. What happened was that the Kraoka mutants won, and a deal was reached between the two that saw mutants from Arakko sent to live on Krakoa, which resulted in many problems due to the differing temperaments of the two societies. Finally, when Magneto realized this wasn’t going to work, the mutants terraformed Mars, and Arakko’s mutants eventually moved there.
4) Days of Future Past (1980)
Days of Future Past was the first X-Men mutant crossover event, but unlike future events, this one didn’t crossover between different books. Instead, it brought the different mutants together in one story, contained within the pages of X-Men (which officially changed the title to Uncanny X-Men in the second part of the story). The book opens in a dystopian world where most mutants are either dead or imprisoned, and the surviving mutants are battling a world dominated by the Sentinels, who have taken over and killed even non-mutant heroes. This world eventually branched off to become known as Earth-811, and the outcome of this story introduced Rachel Summers into the Marvel Universe.
3) Messiah Complex (2007)
Messiah Complex is an X-Men mutant crossover series that puts the team in a complicated situation. When Cerebra (the mutant-detecting device that works alongside Cerebro) detects a new mutant birth in Alaska, the X-Men set out to find the child. This was the first mutant baby born since the events of M-Day, and the X-Men discovered that the Marauders and Purifiers were also hunting for the child. This leads to several revelations, including Bishop admitting that he was sent back in time to kill the baby to prevent a future mutant genocide, and Cable revealing that the baby is his sister, Hope Summers, who he says is the mutant messiah. It also marks a massive change for the X-Men when Bishop tries to kill the baby, but accidentally shoots Professor X in the head, causing Cyclops to officially disband the X-Men. This led to the X-Men relocating to San Francisco, marking the beginning of Messiah War and Second Coming.
2) House of X / Powers of X (2019)
House of X and Powers of X did more to change the X-Men’s world and that of all mutants than any other crossover event in Marvel Comics history. Thanks to learning that mutants always lose in every battle throughout history, Professor X found a way to create a utopia for mutants, where they can live outside of society, inaccessible to humans, and have their own government to rule over themselves. This was on Kraoka, the living island, and he invites all mutants, good and evil, to live there and start their lives afresh. Peace on Krakoa didn’t last, but it was an incredible Jonathan Hickman storyline that spanned five years and created the most complex and interesting X-Men narrative ever.
1) Age of Apocalypse (1994)
When it comes to X-Men and mutant crossovers, Age of Apocalypse is the gold standard. After Legion went back in time to kill Magneto to stop the evil he undertook over the years, he accidentally killed Professor X. This caused Legion to no longer exist. Magneto started the X-Men instead of Xavier. What resulted was a future where Apocalypse conquered the world and created a timeline that was, in turn, tragic and extremely violent. What made this unique was that it ran with the idea of changing everything from the first issue, forcing readers to catch up, similar to later crossover events like Age of Ultron and Age of X. Several mutants came to Earth-616 from this timeline, including X-Man, Blink, Prophet, Sugar Man, and Dark Beast.
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