Character mistake: When Beast is showing Gambit and Rogue the news report about Cannonball, it is shown to be featured in a magazine called Philologist's Quarterly. When Beast leaves the room, he remarks "Ah, there's my 'Philologist's Quarterly'." as if he didn't already see it.
Other mistake: When Wolverine is carving "HERO" into Cocteau's tombstone, he is shown to be using all three claws on his right hand to do so, but the carving looks like it was only carved with one sharp point. If he was using all three claws, each point of articulation for each letter should have been tripled.