This WU mirror-adjacent matchup is a noncreature-spell-heavy control deck full of Force of Will, Ponder, Stifle, and Teferi, Time Raveler, so Deafening Silence is excellent at restricting them to one noncreature spell per turn while we keep deploying creatures. Yorion, Sky Nomad gives us a strong flying blocker and value engine by re-triggering our enter-the-battlefield effects like Skyclave Apparition and White Orchid Phantom. Flickerwisp and Pre-War Formalwear are cut since they're more useful against graveyard or artifact-heavy decks, and we'd rather have proactive disruption against their countermagic-dense list.