Affinity is an artifact-dense deck built around Mox Opal, Kappa Cannoneer, and cheap artifact permanents, so Smash to Smithereens is premium — it answers a key artifact (like Mox Opal or Shadowspear) while dealing 3 to the face, which is huge against their low life total game plan. Rakdos Charm can pick off Mox Opal or another artifact when Smash isn't available. Pyroclasm is a cheap sweeper for their early Pinnacle Emissary tokens and other small bodies. Chandra's Incinerator and Arena of Glory are too slow against a deck that can curve out and kill you before turn 4, so trim them for faster, more targeted interaction.