Sligh is a fast burn deck that can kill from your own life total via Fireblast and Sulfuric Vortex, so Pyroclasm is crucial to reset their board of Jackal Pups, Grim Lavamancers, and Mogg Fanatics in one shot. Swords to Plowshares cleanly answers a Grim Lavamancer or Mishra's Factory before it snowballs, while Auramancer can rebuy a Pyroclasm's Seal-style permanent or block early aggression as a relevant body. Cut slow, mana-intensive cards like Krosan Reclamation and Darigaaz's Caldera along with Elvish Spirit Guide and Squee since you need to stabilize the board, not ramp further. Your life total is a resource against Sulfuric Vortex and Fireblast, so prioritize removing their threats over racing.