Mystic Forge Combo is a mirror-adjacent matchup built on artifact mana rocks and engines like Grim Monolith, Mystic Forge, and Paradox Engine, so Karn, the Great Creator already does heavy lifting by shutting off their artifact activated abilities; Mycosynth Lattice adds more disruption potential by letting us interact flexibly with their all-artifact permanents using our own removal. Ensnaring Bridge can stabilize if they go wide with Construct tokens from their own Urza's Saga, since our hand size will usually be low enough to matter against their token swarm. Eldrazi Confluence is a clunky four-mana answer against a deck that plays efficiently around colorless mana, and Force of Negation is less necessary since their noncreature spells are mostly resolved proactively rather than reactively, so one copy of each is trimmed.