8 Hopelessly Tangled Movie Continuities
6. The X-Men Series

By the time Days Of Future Past came along, the X-Men franchise was in dire need of the timeline being fixed. The numerous continuity errors (how many versions of Emma Frost or Moira McTaggart can there be?) and plot holes had piled up, so Bryan Singer made the wise decision to tidy things up.
Its hard to know where to begin with the timeline before this. For example, Xavier doesnt remember meeting Logan in the original, despite trying to recruit him in First Class. Xavier is also seen walking during a flashback in The Last Stand, despite being crippled in 1962; he also claims to have built Cerebro with Magneto, yet First Class establishes Beast built it without their help.
In First Class, he also has a vision of young Cyclops and Storm, meaning if they were kids in 1962 they should be in their fifties by the time the original trilogy came around. Origins also establishes that Sabretooth is Logans half-brother, while the Sabretooth in X-Men didnt seem to recognise Wolverine and his personality is completely different.
Things aren't even totally consistent post DOFP. The Bolivar Trask from DOFP doesn't bear much resemblance to the one found in The Last Stand, characters like Julibee and Angel were suddenly born twenty years earlier (and the latter has changed nationality), Cyclops should be at least thirty and Styker should like Brian Cox by now.
There are many more lapses throughout the series, but listing them all at once just hurts the brain.