Grixis Affinity plays red spells like Galvanic Blast, so Hydroblast is live, able to counter or destroy it along with any other red permanent they present, which is valuable since Galvanic Blast at metalcraft deals 4 damage and can snipe our key creatures. Blue Elemental Blast and Thraben Charm are left home since diversifying further isn't necessary when Hydroblast alone covers their red cards, and our own artifact-heavy manabase makes Dust to Dust symmetrical risk not worth it. Trim Salt Road Packbeast and Ornithopter, our weakest cards in a mirror-ish race, for this cheap interaction. This matchup comes down to who assembles their affinity curve faster and who can protect their Thoughtcast/Myr Enforcer draws, so prioritize tempo plays.