WU is full of cheap blue spells (Brainstorm, Ponder, Daze, Consign to Memory, Teferi) that Pyroblast can counter or destroy outright, making it a premier answer alongside a second Unholy Heat. Unholy Heat's 2 damage cleanly kills Phelia, Exuberant Shepherd (a 2/2) before it snowballs, and once delirium turns it into 6 damage it can also handle Tamiyo, Inquisitive Student. Force of Negation adds a free way to stop Teferi, Time Raveler or a late Wrath of the Skies while still functioning on our own turn if needed. Ratchet Bomb lets us answer Phelia and Clue tokens from Tamiyo's investigate trigger that Lightning Bolt can't efficiently handle. We trim Flow State and Mishra's Bauble since card selection is less urgent than proactive disruption against this grindy matchup, and Into the Flood Maw and Spell Pierce are weak since Teferi, Time Raveler shuts off our ability to bounce their permanents or Pierce their spells at instant speed on their turn.