The Dark Phoenix (http://en.wikipedia.org/wiki/Phoenix_Force_(comics)) was a cosmic duplicate of Jean Grey, who everyone thought WAS actually Jean Grey, BUT who had actually stashed the real Jean Grey in a cocoon at the bottom of a bay in New York. I'm not explaining anymore than that.
Gamora (http://en.wikipedia.org/wiki/Gamora) joined the Guardians Of The Galaxy mainly because she was having sex with Nova. Maybe she'd have been more excited if she realised signing up would make her a movie star years later.
Rachel Grey (http://en.wikipedia.org/wiki/Rachel_Summers) rejoined Excalibur after a leave of absence in outer space (sure, why not) and decided that wearing the costume her not-quite-Mom's cosmic copy slaughtered a bunch of people in was a good idea because it was a better 'fashion statement'. That last part isn't even a joke.
Jean Grey (http://en.wikipedia.org/wiki/Jean_Grey) died, went to the 'White Hot Room', and started wearing a white version of her old Phoenix costume. Maybe she was planning on getting married?
