Affinity plays a dense artifact manabase (Ancient Den, Seat of the Synod, Vault of Whispers) and numerous nonland artifacts, so Smash to Smithereens is a great two-for-one that both destroys a key artifact land or Springleaf Drum and burns them for 3 extra damage. Relic of Progenitus doesn't stop their artifacts but can be used proactively to exile their graveyard, though its main value here is limited since Affinity isn't graveyard-dependent; it's still a reasonable cheap artifact that can later be sacrificed for value and card filtering against their fast clock. Fireblast's double-Mountain-sacrifice cost is risky against a deck that can punish us for losing lands, so trimming it along with the slower draw spells makes room for more proactive artifact disruption. Keep the core engine intact, since Kessig Flamebreather and Guttersnipe give us a faster, more resilient clock than trying to out-grind their card advantage engines like Novice Inspector and Moon-Circuit Hacker.