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. (00:04:25)
Character mistake: Arkon asks Storm to rule by his side as Empress. After she agrees, he introduces her to the crowd as Queen. (00:19:10 - 00:19:45)
Character mistake: The Colonel states that Hilo, Hawaii is about 120 miles from Pearl Harbor. It is actually more than 200 miles. (00:03:25)
No Mutant Is an Island - S5-E4
Character mistake: When Cyclops demonstrates his power to Rusty to show him that he's also a mutant, he shoots an optic blast at a building and blows a gigantic hole in its facade. While the building had the appearance of being condemned, Cyclops had no way of knowing whether there were squatters inside. He could have seriously injured or killed several people for all he knew. (00:07:35)