Source: marvel.com

7. Oops-Men

The Original Story: Way back when, the X-Men was a phenomenally unpopular comic book, it was almost canceled. But after that great Neal Adams run that everyone forgets about, we got The Uncanny X-Men. Wolverine! Nightcrawler! Storm! Sunfire! The Rest!

In the story, Krakoa, the living Island, captured the X-Men, and Professor X had to assemble a new team of X-Men to go save them. That new team was the Uncanny Squad, who would be just the X-Men for decades afterward.

The Retcon: Turned out that the Uncanny team wasn't the first new team of X-Men Prof Xavier put together. There was also the Deadly Genesis team, which included Darwin. He popped up in First Class, as Vulcan, the third Summers brother. That team went to Krakoa and freed Cyclops, but all of them died doing so.

When Cyke came back to base, Xavier went all whoopsy-daisy and mindwiped Cyclops before sending in another team to definitely die. Only this one didn't. Because it had Wolverine.