Rainbow Dash is my Mare of Swords, or Spears, or Scrolls - I’m still arguing with myself about which it should be. Swords are traditional, Spears seem more in keeping with the weapons in the show. But Scrolls are more of an “Air” indicator - being that they are absolutely about the intellect. In any case, this mare is the analog for the Queen of Swords in a traditional deck - the active intellect which has been made wise by sorrow. She is freedom of thought and clarity of purpose, and the action that transforms thoughts and impulses into reality. Reversed, she is Shakespeare’s Lady MacBeth, using deceit and trickery to gain whatever fanatical goals has struck her fancy. Cruelty emerges, but not from maliciousness - instead this card reversed represents deep disappointments and self-deception, so much so that one can become an ill-tempered mess. Of course, there’s other reversed meanings which make this care more of an emotional and open caring card, but in this deck I see Rainbow Dash both as a perfect example of this card upright, and at her worse, reversed.
 
EDIT: Moved Rainbow Dash to the Knight of Air because she’s too volatile, and I think Zecora makes a better Mare of this suit.