Grixis Affinity has no blue cards in its listed maindeck, so Pyroblast's counter mode is dead, but its destroy-target-blue-permanent mode is also dead — meaning Pyroblast is actually not useful here and should not be boarded in. Dust to Dust is far better: it exiles two artifacts at instant speed-adjacent sorcery timing, hitting their key artifact lands (though Drossforge/Mistvault/Silverbluff Bridges are indestructible, Dust to Dust exiles rather than destroys, so it bypasses that protection), Myr Enforcer, or Refurbished Familiar. Swap plan corrected: bring in Dust to Dust instead of Pyroblast for real impact against their artifact-dense board.