Boros Moxite is a red-white artifact aggro deck, so Blue Elemental Blast and Hydroblast are excellent here, letting you counter or destroy their Lightning Bolt, Galvanic Blast, and other red spells and permanents for one mana. Arms of Hadar sweeps their small creatures: it kills Glint Hawk (2/2) and Sneaky Snacker (2/1) along with any Robot tokens from Melded Moxite, though Kor Skyfisher (2/3) survives the -2/-2. Snuff Out is a liability since paying 4 life is dangerous against a deck full of cheap burn like Lightning Bolt and Galvanic Blast, and Cast Down remains a fine answer to their creatures. Murmuring Mystic's 1/5 body is hard for them to remove and blocks well, but it is slow against a fast deck, so trimming a couple copies for more targeted interaction is worthwhile; Brainstorm and Late to Dinner come out since they do little to interact with the opponent's board in this race.