Mystic Forge Combo is an artifact-based combo deck using Grim Monolith, Lotus Petal, and Urza lands to cast Karn or assemble a big mana turn, so Meltdown for X=1 or X=2 can wipe their Lotus Petals, Manifold Keys, and Giant's Boulders in one sweep. Ratchet Bomb can be set to clear a wave of cheap artifacts once they commit several to the board. Into the Flood Maw and Spell Pierce are weaker here since their key pieces are mostly artifacts (uncounterable by Spell Pierce's noncreature restriction notwithstanding, Spell Pierce does hit noncreature spells including artifacts, but the 2-mana tax is often trivial for a deck with this much ramp) so we prioritize sweeper effects instead. Keep Wasteland in to attack their Urza's Tower/Workshop manabase and slow the combo turn.