Force of Negation is premium against Doomsday, giving you a free way on their turn to counter the Doomsday sorcery itself or setup spells like Personal Tutor. It only hits noncreature spells, so it can't stop Thassa's Oracle. Null Rod turns off Lion's Eye Diamond's activated ability, which can disrupt their key combo turn significantly. Ponder trims since this matchup is about disruption and countermagic rather than digging for your own threats, and Snuff Out is weak since their only real creature targets (Thassa's Oracle, Voice of Victory) aren't the priority compared to stopping the combo. Keep Thoughtseize maximally in since stripping Doomsday or a Lotus Petal pre-combo is often game-ending for them.