Gruul Goblins floods the board with cheap 1-toughness creatures — Goblin Lackey, Goblin Matron, Mogg Fanatic, and the tokens off Siege-Gang Commander — so Pyroclasm's 2 damage sweeps most of their early board, though it won't touch tougher bodies like Goblin Piledriver or Goblin Ringleader. Xantid Swarm buys a turn free of their removal and burn on the attack step, giving you room to assemble Tinker into Phyrexian Devourer and close with Fling. Tsabo's Web is weak since their manabase is almost entirely basics and fetches with only Rishadan Port as a real target, so it comes out along with a City of Traitors since this matchup is fast enough that you want reliable mana rather than a self-sacrificing land. Keep Tangle Wire and Defense Grid in, since both blunt their low curve significantly.