This matchup is decided by protecting your own threats from Stifle/counters and racing before Phyrexian Dreadnought connects twice; there is little dedicated sideboard tech since Naturalize/Warmth are dead against a deck with no artifacts/enchantments or red spells. Tranquil Domain is only relevant if they land Opalescence-style enchantments, which they don't run, so it's largely a placeholder swap and this card stays mostly irrelevant too. Focus on Swords to Plowshares to exile the Dreadnought before it attacks and use Survival of the Fittest to find Ravenous Baloth or Deranged Hermit for board presence. Keep the plan minimal since almost nothing in the sideboard is well-positioned here.

Warmth is a premier answer to Mono-Red Sligh, gaining 2 life every time they cast Lightning Bolt, Incinerate, Flame Rift, or Fireblast, directly countering their damage race plan. Their deck has almost no way to interact with an enchantment (no artifact/enchantment removal in the listed sideboard), so Warmth sticks reliably. Quirion Ranger and Wall of Roots are cut because they don't meaningfully block or race Black Vise/Mishra's Factory pressure, and this matchup rewards stabilizing life total over incremental mana development. Use Swords to Plowshares proactively on Grim Lavamancer to deny repeated damage sources.

Naturalize is excellent here, destroying Solitary Confinement, Serra's Sanctum-enabling enchantments, Sterling Grove, Enchantress's Presence, or Opalescence to disrupt their engine before it snowballs. Tormod's Crypt has minimal upside against their plan but can strip Replenish-adjacent graveyard value if they mill themselves; keep it in as a low-cost inclusion. Wall of Roots and two Quirion Rangers are cut since this matchup is about proactive disruption and racing with Survival of the Fittest into big threats, not blocking. Prioritize using Naturalize on Sterling Grove to strip the shroud protection it grants their other enchantments, or on Solitary Confinement to remove their lock piece when it is not protected by Grove.