Boros Moxite is red-white, and its only blue card is Sneaky Snacker, which its red-white mana can't realistically cast and which only shows up when it returns from the graveyard. Pyroblast and Red Elemental Blast therefore have almost nothing to hit, and they stay in the sideboard. Smash to Smithereens is good here since the deck runs many artifacts like Melded Moxite, Lembas, Ragged Short Spear, and the artifact lands Ancient Den and Great Furnace. Destroying one while dealing 3 damage to the opponent adds real tempo and reach in a race against their Glint Hawk/Kor Skyfisher value shuffle. Rustvale Bridge is indestructible, so don't aim Smash at it. Keep the core burn-and-discard engine intact since this is an aggro mirror where speed and efficient removal (Lightning Bolt, Fiery Temper) on their small creatures like Glint Hawk matter most. Trim the slowest card-advantage spells to make room for the artifact disruption.