This opponent is packed with counterspells like Counterspell, Foil, Thwart and Daze, plus Stifle, which can counter Hermit Druid's activated ability or the abilities Volrath's Shapeshifter copies. Xantid Swarm, when it attacks, stops the defending player from casting spells that turn, which can buy a window to resolve Hermit Druid or combo off without fear of Counterspell, Foil, Stifle, or Daze. Duress only hits noncreature, nonland cards, which does include their countermagic, but it takes a single spell, so we trade one copy for the Swarm to improve our ability to push through disruption. Keep the rest of the maindeck intact since our clock is faster than theirs if we resolve the combo.

Note: this opponent's description mentions Madness/Wild Mongrel but the actual mainboard listed is Goblins aggro with Goblin Lackey, Piledriver, and Siege-Gang Commander, so treat the printed mainboard as ground truth. Pyroclasm deals 2 damage to each creature, ours included, and it wipes their swarm of 1/1 and 1/2 Goblins, including Siege-Gang tokens, plus most of their small creatures like Mogg Fanatic and Goblin Lackey. That is excellent against a go-wide strategy. It is not one-sided, though. It also kills our own small creatures such as Birds of Paradise, Hermit Druid, Volrath's Shapeshifter and Psychatog, so cast it before committing those to the board and don't rely on it once the combo pieces are already out. We bring in all three copies to blunt their early rush, trimming Duress (less useful against a deck with few key noncreature spells) and two of our weaker mana sources to make room. This matchup comes down to surviving their early rush long enough to find Hermit Druid or Survival into the combo.

Enchantress decks have little interaction beyond Swords to Plowshares, Abeyance and Parallax Wave, so Xantid Swarm lets us attack and shut off their ability to cast Swords or Abeyance the turn we try to combo. It doesn't stop Parallax Wave or Seal of Cleansing, since those are activated abilities rather than spells. Naturalize answers Solitary Confinement or a key enchantment like Sterling Grove if the game goes long, since they have very little pressure early. Duress stays in, because it can take Swords, Abeyance, or a key enchantment like Opalescence or Replenish before they come online. To make room we trim an Elvish Spirit Guide and two Wall of Roots, the most replaceable mana sources against a deck with no real pressure or disruption of our hand. This matchup is winnable on raw speed if we resolve the combo before their engine spirals out of control.