The Barbie Adventure VIII: Barbie in the 12 Dancing Princesses

Starlight knows. She now knows everything.
Upon seeing the seven Equestria Girls leaving their last movie, they have no choice but to spill their story. Of course, she insists on going too, saying she can replace Rainbow Dash temporarily (as she's down for the count currently). And so they do.
Now in the movie world, they meet 12 sisters and their father, King Randolph. And as a twist, Randolph's mind has changed to believe that the newcomers are just seven more of his daughters. Even the sets and plotlines change to add to this effect.
Of course, the 12 sisters are quick to figure out the truth, just as Randolph brings in his cousin, Duchess Rowena, to turn them into "proper princesses." Rowena takes away everything the girls love. But one night, they all uncover a magical world, where they can dance to their hearts content. Starlight finds herself falling in love with a fantastical movie world she doesn't want to leave.
But like with the golden pavilion, all good things had to reach an ending.
And in the case of the movie, they have to stop Rowena before she poisons Randolph and takes over the kingdom.