Source: nerdist.com

5. Jean Grey’s Anatomy (was Probably That of a Giant Bird Made of Fire)

The Original Story: As they returned from space, the X-Men encountered serious radiation, and only Jean could stay at the controls to pilot the ship down. At that time, she was possessed by the Phoenix Force, and became The Phoenix. After the shuttle crashed into the water, she emerged with a great new costume and some sweet powers.

But those powers were too much. They drove her to the breaking point, and, after some mindf***ing on behalf of the Hellfire Club, she flipped a switch and became the Dark Phoenix. And ate a star. She regained enough control to commit suicide to prevent committing even more space-murders.

The Retcon: Except not, because it turned out that the Phoenix Jean Grey wasn't actually Jean Grey. It was the Phoenix bird, who stuck Jean in a cocoon under the Bay and took her place. The Avengers found the real Jean, the Fantastic Four brought her back, and she joined X-Factor. And then she died years later, because Jean Grey was mortal.

It's just what she does.