Grixis Affinity's red cards, Galvanic Blast, Krark-Clan Shaman, and Makeshift Munitions, are the only legal targets for Hydroblast, which counters a red spell or destroys a red permanent. Myr Enforcer, Utrom Monitor, Refurbished Familiar, and their artifact lands are colorless, blue, or black, so Hydroblast can't touch them. That makes Hydroblast a focused answer to their burn and Shaman rather than a catch-all. Faerie Macabre can discard to exile up to two cards from graveyards, including the creature cards Blood Fountain wants to return to their hand, and it is also a 2/2 flyer if you want a body. Trim the slower spells (Stream of Thought, Embrace the Paradox, some Preordain) since this matchup is about surviving their early rush and answering specific threats rather than grinding long. Keep your full Fog suite, since their affinity-discounted curve-outs still need to be neutralized in combat.