Doomsday is a pure combo deck looking to resolve Doomsday and then Thassa's Oracle for the win, so Force of Negation is your best tool to stop the Doomsday sorcery itself or a follow-up Personal Tutor. Consign to Memory can counter Thassa's Oracle's enters-the-battlefield triggered ability outright, which is a clean, efficient answer to their win condition. Ghost Vacuum lets you proactively exile pieces from their graveyard or hand disruption fallout to disrupt Street Wraith-fueled setups. Stifle has few valuable targets and Flow State is too slow to matter before they combo off, so both are cut for the extra interaction.