WU is a tempo/control deck with Phelia, Exuberant Shepherd, Tamiyo, Inquisitive Student, and Teferi, Time Raveler providing card advantage and disruption, so Force of Negation lets us proactively stop Teferi or a key noncreature spell on their turn for free. Dauthi Voidwalker provides an evasive clock: shadow means it can be blocked only by creatures with shadow, and none of their creatures have it, so it can't be blocked. It is still vulnerable to Swords to Plowshares, but while it lives, its exile effect also keeps cards out of their graveyard, which hurts Snapcaster Mage. Mockingbird loses value since their best creatures (Tamiyo, Phelia) aren't great copy targets, and Ponder is less needed since this matchup is more about resolving and protecting threats than deep card selection. Keep Daze and Force of Will in since this matchup is heavily contested on countermagic.