Grixis Affinity's Galvanic Blast is a red spell, making Hydroblast a premium answer: it can counter Galvanic Blast and can also destroy their red permanents, Krark-Clan Shaman and Makeshift Munitions. It cannot touch their artifact lands or artifact creatures like Myr Enforcer and Refurbished Familiar, since none of those are red. Dust to Dust can two-for-one their artifact engine, hitting key pieces like Ichor Wellspring or a cheap-cost Myr Enforcer/Refurbished Familiar. Snuff Out loses value since many of their creatures are small and die to anything, Refurbished Familiar is black so Snuff Out can't even target it, and paying 4 life is risky against a deck that can burn you out with Galvanic Blast (which deals 4 with metalcraft); Archaeomancer is too slow against their fast affinity curve. Prioritize killing Refurbished Familiar and Myr Enforcer on sight, before affinity makes them cheap, and use Hydroblast proactively on Galvanic Blast when it threatens lethal.