Grixis Affinity floods the board with cheap artifacts like Ichor Wellspring, artifact lands, and affinity-reduced Myr Enforcer and Refurbished Familiar, so Cast into the Fire's exile-artifact mode is strong removal against a key piece like Blood Fountain or an artifact land they need for affinity, while its damage mode deals 1 damage to each of up to two target creatures, which can pick off Krark-Clan Shaman and a Refurbished Familiar (2/1) in one shot. Gorilla Shaman's activated ability can blow up their noncreature artifacts, including artifact lands like Seat of the Synod or Vault of Whispers (mana value 0, so X=0) and Nihil Spellbomb, denying affinity count. Since their own Galvanic Blast gets even better with metalcraft, racing is risky, so lean on this disruption to deny their affinity costs and board state. Trim slower or less flexible pieces for this proactive answer suite.