Boros Aggro is a mirror-style race full of efficient threats like Voice of Victory, Momo, Friendly Flier, and Magmatic Hellkite, so protecting your own creatures from their burn (Burst Lightning) with Shore Up and Secret Identity keeps you ahead on tempo. Spell Pierce can stop key noncreature spells like Burst Lightning or Erode when they're tapped out developing. Since this is a race, we trim slower pump spells that don't add pressure or protection quickly enough.