Bria, Riptide Rogue Bria, Riptide Rogue does a whole lot for the deck
The first thing you pull out of the boxes is a giant rule book with large font and short pages that explain the most basic, barebones mechanics
Oh, and in any deck where your Commander is at least Blue and Green, this is strong as you cast and recast your leader and net serious bang for your triggering buck
You might also need to get rid of a problematic creature such as Elesh Norn, Mother of Machines without worrying about the possibility that shell immediately be reanimated out of the graveyard
Starting Town and Multiversal Passage will see tons of play from this point forward, with a nod towards Passage for actually picking up basic land types
However, if you want to complete your collection, you might as well pick one copy up from Ursula's Return