Grixis Affinity is red-black-blue with heavy artifact synergies, but Hydroblast and Blue Elemental Blast only hit red permanents and spells. In this matchup that means Galvanic Blast, Krark-Clan Shaman, and Makeshift Munitions, so Hydroblast is a narrow but live answer: counter a Galvanic Blast or destroy a Krark-Clan Shaman, even though the deck's real engine is colorless artifacts. Relic of Progenitus is the stronger inclusion, disrupting graveyard-based value like Blood Fountain returning creatures to hand, while also exiling all graveyards for a one-mana draw later. Plunder the Trollshaws is too slow against a deck that curves out fast with cheap artifact creatures, and Dispel is a narrow answer, so they're cut for more proactive disruption. Prioritize Cast Down on Refurbished Familiar, since it is black and Snuff Out can't target it, and save Snuff Out for Myr Enforcer before it attacks.