Rose Tyler bounce's across the multi-verse, and recruits some allies- namely, herself.
I figured since Rose bounced across the multi-verse for god knows how long, she had to have met some parallel version of herself, and no matter what reality how is Rose Tyler supposed to meekly step aside while her universe is at stake!
This must crossover with AT LEAST ONE of the following: The Marvel-verse (comics, movies, whatever), Star Wars, Star Trek, Mass Effect, Supernatural, and Buffy the Vampire Slayer. Preferably all of them, or anything else you can think of.
Bonus points if each version of rose has a human alternate reality version of the Doctor, but only one of them has a version of the tenth Doctor. Even more bonus points if Star Wars Rose is a smuggler, and Star Trek Rose is a Vulcan.
Message me if you have/want to write it!