Pyroclasm's 2 damage sweeps their mass of 1-toughness Goblins (Lackey, Matron, Warchief, and the tokens from Siege-Gang Commander), punishing their go-wide plan. Pyrokinesis, castable for free by exiling a red card, flexibly clears multiple small Goblins or removes a key attacker like Goblin Piledriver. Sulfuric Vortex is a liability in this fast mirror-speed race since it damages you as much as them, and Urza's Bauble is too slow against their explosive curve. Hold Pyroclasm until they've overextended, since Goblin Matron and Ringleader let them rebuild quickly.