It just so happens to do so by helping synergize with your strategy
You see, when you attack with Ghalta and Mavren out, you get two options to choose from as an attack trigger
If it's a token or play aide, it will often have an ad on the back (assuming the play aide isn't double faced)
As Perdita, Devoted Mother activates her ability as soon as she enters play, youll effectively have a nice little bodyguard to protect her with
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of Serah Farron or Crystallized Serah's first abilities)
By learning a few simple rules, it quickly becomes very easy to distinguish the rarity of a Magic: The Gathering card