In Avengers: Infinity War, Thanos got the chance to make his way through all the heroes of the Marvel Cinematic Universe on his path to claim the Infinity Gauntlet. However, the X-Men weren't available to be used in the MCU, none of the mutant heroes appeared in the adaptation of Jim Starlin, George Perez and Ron Lim's Infinity Gauntlet, even though they played roles in the original story.
Even though some of the X-Men's most iconic members were around for the Marvel Universe's original Infinity Gauntlet saga, things didn't exactly go well for any of Marvel's mutants in that story. Now, we're going to take a closer look at how Thanos wiped the floor with the X-Men in the iconic crossover.
After Thanos takes the Infinity Gauntlet and the six Infinity Gems for himself, he gains enough power to instill his will onto the entire universe. He soon tries to appease his mistress Death by using the Gauntlet to kill half of all life in the cosmos, snapping his fingers and impacting all of existence near the start of the crossover. This effect hits Earth and kills numerous heroes and villains instantly. Captain America rallies the remaining heroes so they can over a plan and figure out what happened to the universe, and how to try and reverse it.
While considering which heroes have gone missing following the Snap, it's confirmed that mutant heroes like Firestar and Quicksilver, most of X-Factor -- Jean Grey, Beast, Archangel and Iceman -- and almost all of the X-allies Alpha Flight -- Vindicator, Guardian, Box, Puck, Northstar, Shaman and Sasquatch -- are among the people who disappeared. Other mutant teams like Excalibur and many members of the X-Men are missing in action and do not accompany their allies into battle against Thanos, meaning they were likely also casualties of Thanos' actions.
When Doctor Strange calls upon all remaining heroes to come to their aid, the only major mutant heroes left to join the offensive against Thanos are Wolverine, Cyclops, Namor and Scarlet Witch, who was thought to be a mutant at the time. Wolverine is even approached by Adam Warlock specifically, who asks him and Hulk to be willing to murder Thanos if given the chance.
All four try to participate in the final battle against Thanos, alongside the rest of the heroes. And like their fellow fighters, the mutant heroes are wiped out fairly easily by the omnipotent power Thanos possesses thanks to the Infinity Gauntlet.
Despite the best attempts of the heroes and a well-executed plan, Thanos is just too powerful to be beaten. When Namor and She-Hulk attack Thanos, Thanos attaches a spore to their chests that quickly grows across their bodies and suffocates both of them. Wolverine is able to use the chaos of the battle to sneak attack Thanos, and even embed both sets of his claws deep into the Mad Titan's chest. But the blow doesn't kill Thanos, and he's able to use the gauntlet to turn Wolverine's adamantium skeleton to rubber - reducing Wolverine to a quivering body on the ground.
Cyclops and Scarlet Witch try to overwhelm Thanos together, blasting him with their full power at the same time. Focusing on Wanda first, Thanos reduces her to atoms by seemingly deflecting her own hex powers onto herself. Cyclops actually feints Thanos into opening himself up for an attack from Iron Man, but Iron Man is attacked by Terraxia, Thanos' ally. Now giving the mutant leader his full attention, Thanos encases Cyclops' head in a clear but impenetrable box, stopping off his blasts and cutting him off from oxygen, leaving him to die despite Captain America's best efforts to free him. With that, the last active mutant heroes of the Marvel Universe die, as Thanos continues to carve a path of destruction through Marvel's remaining heroes.
Despite their cruel fates, all of these mutants were restored to life at the conclusion of the storyline, along with everyone else Thanos killed. Although it's unlikely that the X-Men could have affected the events of Avengers: Infinity War and Avengers: Endgame any more than they did here, but it's worth remembering that they got the chance to try and make a difference in the battle against Thanos in the original Infinity saga.