Clarion Conqueror turns off activated abilities of artifacts, creatures, and planeswalkers, which shuts down Mystic Forge's cast-from-top ability being fed, Grim Monolith's mana ability, The One Ring's draw engine, Manifold Key, Voltaic Key, and Karn, the Great Creator's abilities all in one card. Rest in Peace exiles the graveyard on entry, which is low-impact on their main engine but still denies any Kozilek's Command graveyard exile value and incidentally removes our own Chalice-style symmetrical risk from the equation. Chalice of the Void is dangerous to keep in since this opponent runs many 0-cost artifacts (Lotus Petal) and relies on X spells of its own, but more importantly we share mana value overlap with our own Lotus Petal and Chrome Mox, so it's safer to prioritize Clarion Conqueror's blanket shutdown; Sheltered by Ghosts is cut since Clarion Conqueror already locks down their most important permanents more thoroughly. Witch Enchanter stays in the mainboard as premium answer to their many key artifacts.