Spoilers for X-Men: Days of Future Past, obviously. I finally watched the film today, and while I did like it, I didn't find it to be the great film others made it out to be. Your mileage may vary. Personally among all the Marvel-related films, I'd rank it just below X-Men: First Class, and I would rank both DoFP and FC just above either Hulk film.
So, let's look at some of the continuity errors and how they might be explained away. To be clear, these are No Prize-type fan explanations, as the actual film creators didn't seem to notice (or care about?) these errors when making the films.
Emma Frost - Alive? Young again?
As I mentioned in an earlier comment, even though Emma Frost was played by a 34-year-old in 1962, and a 23-year-old in the 1980s, and declared dead by the 1973 events of DoFP, this does not necessarily mean a contradiction.
In the comics, Emma Frost was cloned by the Weapon Plus program - the same program that created Weapon X. The clones, part of Weapon XIV, are collectively called the Stepford Cuckoos and currently pal around with their genetic progenitor in the pages of Uncanny X-Men.
Professor X and Magneto - Why doesn't history match?
Then there's the Obi-Wan conundrum.
Why does the Professor's stated account of events differ so wildy from what fans saw in X-Men: First Class? Rule one of Professor X: The Professor lies.
For the record, we do know Xavier and Magneto met about 15-to-20 years before the events of X-Men #1 (1963) because of the flashbacks from Uncanny X-Men #161 (1982), but these were things in Xavier's memories. Xavier has repeatedly tampered with the memories of others - even erasing an entire team of X-Men from history and framing an innocent mutant island for megalomania in X-Men Deadly Genesis (2005) - but also his own.
Back in the early 60s when Stan would throw everything at the wall to see what sticks, he established that middle aged Professor X was secretly in love with his teenage student. So yeah, this was quickly dropped (although it did come up again later). Then in X-Men #53 (1996), Jean Grey learned of this hidden crush and that Xavier messed with his own mind to suppress it.
The "first" X-Men - Who the when now?
Sure, Prof said Cyke, Storm and Jean were his first X-Men, but were they? In the comics, Cyclops has often been called the "first X-Man" because he was the first trained to put on the suit. But later retcons revealed Xavier had been teaching Jean Grey since she was little (making that "crush" even creepier), and later still we learned that Xavier had taught Amelia Vought before even Jean Grey (and yes, he dated her too). Then, in 2011, fans were introduced to the new "First" X-Men. This team, assembled by Wolverine just before entering Weapon X, was the first team of young mutants guided by Xavier - until the next retcon anyway.
Sabertooth - What's the deal with Victor Creed?
First off, despite the fact it makes perfect story sense, in the comics Wolverine and Sabertooth are not actually related. They do, however, have a lot in common.
Sabes and Wolvie are both about 100 years old, both from Canada, and of course, have similar powers. They were also both subjects of the Weapon X program. While Wolverine was given Adamantium, Sabertooth's already amped physique was given a major boost, and both mutants had their histories wiped and replaced with various memory implants. While Wolverine has worked through most of his memory problems recently, it's unclear how much Sabertooth knows of his own past (including the ones shown here from Wolverine #63 (1992).
In the films, Sabertooth was Wolverine's brother and was actually a pretty competent fighter before the Weapon X program. It's clear from the existence of Deathstrike in X2 that the Weapon X program continued after X-Men Origins: Wolverine, so it's possible, albeit unconfirmed, that Sabertooth reentered the program, gained his greater strength (at the cost of his intelligence) and lost his memory.
Mystique - Why don't she and Xavier hug and make up?
In All-New X-Men #27, which came out a few weeks ago, we learn that Mystique and Charles had some kind of very intimate connection that was never before revealed.
Is it so strange that characters from comic books (or any other soap opera-type episodic fiction) would have secret pasts that don't come up everyday? Or for that matter, that two people who haven't been friends in 30 years would not be keen on reliving old grudges every time they meet?
That's all I got on that.
Professor X - How is he still alive?
So Professor X died in X-Men: The Last Stand. If you waited for the after credits scene, you know his mind survived in a new body.
In the comics, Xavier has died (or pretended to) several times, but most notably when the Brood aliens infested his body, his mind was transferred into a fresh cloned body. Other mutant telepaths, including Xavier's embolized twin Cassandra Nova and the ancient evil Shadow King often take over new bodies and use their powers to make people believe the new body looks like their original. Whether Beast or another superscientist whipped up a new body or Xavier just wants to look like his old self, this is something the comics have dealt with before.
By the way, can we just pause for a moment to consider that Charles Xavier - as a fetus - took it upon himself to kill his own twin sister? That's messed up.
The Summers family - A headache all by itself
Leaving aside for a moment how complicated the Summer's family tree is (image by Geckobot), how could Alex Summers be a teen in the 1960s, and Scott Summers be a teen in the 1980s?
Different possibilities here:
- Space travel, because relativity will screw with you. In the comics, the Summers clan was abducted by aliens (because of course they were) while the boys were young. Their father met the boys later when both had reached adulthood (but the dad had barely aged).
- Time travel, because causality's for chumps. Just about every prominent member of the Summers tribe has traveled through time. At this point, Cyclops is in his mid-30s, his son Cable is in his 60s, his grandaughter Hope, who was born a year ago, is 18, and Cyclops' 16-year-old self is palling around the galaxy with their dad Corsair, who looks like he's in his 40s. Go figure.
- They aren't brothers, because movies. As already established, Sabertooth and Wolverine have different relationships in the movies and comics, why not Alex and Scott?
Moira and Trask - How can the ages/ethnicities be different?
So Moira was Scottish and Trask was African American in the present, both adults and certainly not elderly, and yet in the past Moira was American and Trask was anglo (not to mention played by an underutilized Peter Dinklage). The Moira situation is silly (as any of these continuity errors could and should have been easily avoided), but it can have the same answer that the Trask situation easily provides.
Why should the Trask in X3 be Bolivar Trask from DoFP? Several members of the Trask family have appeared in comics, including Donald Trask III from New X-Men #114 (2001) who was so distantly related that he was only vaguely aware of his family's connection to Sentinels. Maybe that was the Trask we saw in X3.
Sentinels - Where were they all this time?
While the movies have yet to show us a good fight between classic Sentinels and mutants (even if the Nimrod Sentinels from the future were pretty cool), apparently they've been causing each other problems in between X-Men films.
The brief simulated fight between Sentinels and the X-Men from X3 shows that the team had encountered the giant robots before (even if audiences didn't get to actually see the robots), and Stryker's computer files uncovered by Mystique in X2 included information on Project: Wideawake. In the comics, Project: Wideawake was a secret government program funding, among other things, experimental Sentinel research. According to DoFP, Trask industries and the government had secretly been developing the program for years, and Stryker knew about it from day one.
Kitty Pryde - She can do what?
In the classic storyline starting with Uncanny X-Men #141 (1981), on which this film was nominally based, Kitty Pryde has her mind sent back in time by Rachel Summers (later Grey) into the body of her younger self to stop Mystique from assassinating a politician, a move that would spark anti-mutant paranoia and lead to the Sentinel-dominated future. Of course, the same politician would get assassinated years later anyway, but watchyagunnado?
In the movie, Kitty Pryde sends Wolverine's mind back for basically the same mission.
How does she do it? I'm sure there's some physicsy sounding reason that could tie her ability to phase between atoms (between reality?) as a precursor to her ability to phase through time, but in the comics, whenever a mutant starts exhibiting strange new powers, they just chalk it up to a "secondary mutation." That's why the Beast was briefly a cat person, Emma Frost could suddenly turn into a diamond and Archangel became a walking healing potion.
It seems this is Kitty Pryde's new power in the movie version.
I sure bet there are, but for all these continuity faults (and there are so, so many), many if not most can be overlooked.
Of course, that doesn't make any of the X-Men movies good - that's up to the viewer to decide.