Missing sideboard cards? The full 15-card sideboard runs about $38.35.
Buy sideboard on ManapoolHydroblast counters or destroys red spells/permanents for one mana, directly answering Kessig Flamebreather, Guttersnipe, Fiery Temper, and Lightning Bolt. Dispel cheaply protects our board or stops a burn spell aimed at our face during the race. Faerie Miscreant's 1/1 body dies to nearly every card in their deck and rarely finds a second copy fast enough, while Essence Flux is too slow when every mana needs to go toward pressure or interaction. This matchup is a race, so prioritize efficient interaction over card advantage.
Envelop counters their key card-advantage sorceries like Lorien Revealed, Ponder, and Sleep of the Dead, disrupting the graveyard-filling engine that powers Tolarian Terror and Cryptic Serpent. Dispel protects our own Counterspells and tempo plays from their Dispel/Counterspell suite in this counter-heavy mirror. Steel Sabotage stays in the board since Tolarian Terror and Cryptic Serpent are cast as creature spells, giving it no legal target. Essence Flux and Harrier Strix are cut for being too passive when we need mana open for counterwars.
Steel Sabotage counters or bounces key artifacts like Expedition Map, Giant's Boulder, and Bonder's Ornament that fix their mana and ramp toward Tron. Envelop counters their crucial ramp and card-selection sorceries like Ancient Stirrings and Malevolent Rumble, slowing their assembly of Urza's Tower, Mine, and Power Plant. Essence Flux does nothing productive against their game plan, and Snap is weak since bouncing their few creatures doesn't address the land-based engine. Speed and proactive disruption of their mana assembly matter most before they reach a critical mass of colorless mana.