One noteworthy fact about the X-men is that a lot of their storyline involved time travel in some shape or form. Many of these storylines involved a member of the X-men messing up the timeline for a variety of reasons. Some of these changes involved the timeline being overwritten by a darker more dystopic timeline like in the "Age of Apocalypse" storyline. Other storylines involved an X-man trying to prevent one from occurring.
This article will examine ten X-men who have made changes to the timeline and ranked them based on how damaging these changes were to the timeline. This article's criteria will be based on how negative these changes were to the timeline.
10 Shadowcat
The earliest example on this list would be Shadowcat from the "The Day of Future's Past" storyline. This storyline sees Shadowcat from a Sentinel-ruled future travels back in time to prevent the assassination of Senator Robert Kelly that created this dark future.
While Shadowcat did succeed in her efforts to change the future, it did not particularly change the timeline to the extent that other X-men have. This lack of change in the timeline is that while Shadowcat prevents the immediate cause for her dark future, the possibility of a similar future occurring still exists.
9 Moria MacTaggert
The most recent example on this list, so recent that the full extent of changes to the timeline is not yet fully seen, is Moria MacTaggert. Johnathan Hickman's House/Power of X miniseries reveals that the longtime X-men ally was secretly a mutant with the ability to relive her life with knowledge from previous cycles. She used this ability to try and create a timeline where mutants are not wiped-out by mankind's technologically creation.
Due to this reveal occurring rather recently, it is hard to know the full damage of her efforts to shape the timeline. The only thing that is known right now is that Moria's effort has created the current X-men status quo of a united mutant nation on Krakoa. This also not the only that she played a major role in altering the timeline as she helps Legion to alter the timeline into briefly the Age of X timeline
8 Cable
The most famous time-traveling X-men would have to be Cable, Cyclops' son raised in a dark future ruled by Apocalypse. Seeking to prevent Apocalypse's rise, Cable travel backs to several decades in the past where he started work as mercenary and sold off some of his futuristic weapons to begin this endeavor.
Unlike other examples on this list, Cable's damages to the timeline are more implied than stated outright. For example, the fact that Cable sold some of his futuristic weapons to several sellers several decades ago is the reason why some criminals and organizations have access to more advanced technology than they should. He also played a role in several storylines that altered the timeline in some way or another.
7 Multiple Man
While Multiple Man has time-traveled on several occasions, including one mention later on this list, the most damage he did to the timeline would be in his 2018 solo miniseries. This series sees one of Multiple Man's duplicates seeking to cheat death by using a time travel device to travel into the future. This effort would create a dangerous time loop.
This time loop results in a future ruled by a tyrannical Multiple Man who is then killed by a younger version of himself. This time loop created havoc upon the timeline leading to an invasion of evil Multiple Men from the future invading the present. This chaos was only stopped by Multiple Man absorbing all the different versions of himself.
6 Bishop
Bishop is in a similar camp as Cable of being a time traveler from the future trying to change past, who is also a long time member of the X-men. Like Cable, his technology causes problems as his time travel device has been stolen by several people trying to change the timeline. Unlike Cable, Bishop had made some more noticeable changes to the timeline.
Firstly Bishop's presence during the Onslaught storyline allows him to prevent the X-men's death at the hand of Onslaught in his timeline. Bishop would also later shoot Professor X, trying to capture Hope Summers, viewing her as a potential cause for the dark state of his future.
5 Layla Miller
Layla Miller has been changing the timeline since her first appearance in the House of M, where she played a key role in restoring the timeline to its default state. Layla Miller would, however, mess up the timeline even more during Peter David's second X-Factor run. This series finds Layla Miller stranded in Bishop's future, where she played a major role in the Summer's Rebellion.
Layla Miller's most impactful action during her time in the future would be through bringing Trevor Fitzroy back from the dead. Due to how her mutant powers work, Trevor Fitzroy was brought back without a sense of morality. This lack of morality allowed him to travel back in time causing both Bishop to become stuck in the present, but also set the stage for Emma Frost to turn away from villainy.
4 Wolverine
It wouldn't be an X-men list without Wolverine being somewhere in there. In this case, it is a Wolverine from a future devastated by Ultron taking over the world during the Age of Ultron storyline. This dark future leads to Wolverine and the Invisible Women to travel back in time to kill Hank Pym preventing Ultron's creation.
While Wolverine succeeded in killing Hank Pym, it had the unforeseen consequence of creating a present-day where an alliance of Doctor Doom and Morgan le Fey have taken over the world. Wolverine would later try to fix these changes, which succeeded in restoring the original timeline also lead to Galactus devastating the Ultimate Universe.
3 The Original X-men
For a long part of the 2010s, the five original X-men were sent forward into the present causing a bunch of problems for Marvel's timeline. Most noticeably that if any of them died, it would massively damage the timeline creating several irreparable alterations to history.
The continued presence of the original five caused not only one, but two dark future. The Battle of The Atom crossover shows a future where the original five cause Cyclops' and Wolverine's X-men's conflict to reach a violent conclusion. The EXtermination crossover shows another future where the death of the time-displaced Iceman creates a timeline where mutants are hunted to extinction by cyborg monstrosities.
2 Scarlet Witch
Unlike other examples on the list, Scarlet Witch altered the timeline not through time travel but by altering the timeline itself. The extent of this ability can be seen in her creation of the House of M reality. This reality was created by Scarlet Witch altering the timeline through making Mutants emerge earlier in the recent past allowing for Magneto to take over the world.
House of M's damages to the timeline was not just limited to just briefly overwriting the present, but Scarlet Witch bringing the timeline back to normal also damaged the timeline. Scarlet Witch brought the timeline back to normal by altering reality to strip a majority of the world's mutants of their powers leading to a status quo still affecting the X-men titles today.
1 Legion
The winner for X-men that has most damaged the timeline would go to Professor Xavier's son Legion. He is responsible for overwriting the timeline with a darker alternative on two occasions.
Most famously he created the Age of Apocalypse by accidentally killing Charles Xavier during a time travel attempt to kill Magneto before he became a supervillain. He also played a role in creating the Age of X dimension by inspiring Moria MacTargget to alter the timeline to prevent the X-men from forming so that he could be the savior of mutant-kind.