Doomsday wants to resolve a clean Doomsday and then win with Thassa's Oracle (with help from Lion's Eye Diamond), so the extra Force of Negation copies are our best way to counter the Doomsday itself or other noncreature setup spells for free on their turn. Force of Negation can't stop Thassa's Oracle, since it's a creature spell, so the Doomsday is the key target. Barrowgoyf is a cheap lifelink/deathtouch threat that pressures their low life total (Doomsday makes them lose half their life, and fetchlands and Street Wraith cycling cost them more) while being hard for them to profitably block or race. We cut Eldrazi Confluence since countermagic and proactive pressure matter far more than a flexible instant here, and we trim slow ramp artifacts since this matchup is decided by disruption and clock speed, not mana development.