Doomsday is a pure combo deck trying to assemble a five-card stack ending in Thassa's Oracle to win outright, so disrupting their ability to cast spells is paramount. Deafening Silence is devastating here since their entire turn revolves around chaining multiple noncreature spells (Dark Ritual, Ponder, Brainstorm, Doomsday itself) to find and execute their combo in one turn. Containment Priest doesn't stop Thassa's Oracle since it's cast normally, but it's still a fine flash blocker and curve filler. Flickerwisp and Pre-War Formalwear are cut as they provide no meaningful disruption to a combo plan that doesn't care about board state.