Very quick and easy trophy to obtain - Head into Arcade, Versus or Survival mode and select Unknown as your fighter and anyone else for your second (It does not matter), As soon as you are in the fight press the tag out button which by default should be
or
and you will switch to your other fighter, Now keep switching using the tag button and everytime Unknown comes back out she will have a new move set.
Sometimes her moveset will repeat itself but keep switching characters and within seconds you will get the trophy.