Boros Aggro is a mirror-style race full of resilient dragons (Magmatic Hellkite, Nova Hellkite) and Burst Lightning of their own, so Sunspine Lynx's static anti-lifegain and damage-on-entry trigger is great against their heavy nonbasic manabase while adding a sticky 5/4 body. Sear's 4 damage reliably kills their Momo, Friendly Flier-boosted or Sarkhan-fueled threats that Burst Lightning alone can't always answer. Impractical Joke caps too low against their bigger dragons, and Secret Identity doesn't block well against their flying-heavy attackers. This matchup is a race — prioritize removal that trades up and keep your clock as fast as possible.