Doomsday is a fast combo deck that wins by resolving Doomsday and then triggering Thassa's Oracle, so your primary goal is to prevent Doomsday from ever resolving. Disruptor Flute naming 'Doomsday' is the single most powerful hate piece in this matchup, as it makes their entire game plan impossible to execute while still being a 0-cost artifact that fuels your engine. Chalice of the Void on one is also backbreaking, simultaneously shutting off Brainstorm, Ponder, Dark Ritual, Daze, and Consider, which cripples both their velocity and their protection. Force of Will and Consign to Memory serve as backup permission—notably, Consign to Memory can counter Thassa's Oracle's triggered ability on the stack even if a Doomsday somehow resolves, giving you a hard answer to their finish. Deploy your threats through Ancient Tomb and Mox Opal as quickly as possible, since a fast clock forces them to try comboing through your interaction rather than setting up safely.