UBG Reanimator wants to cheat Griselbrand, Atraxa, Grand Unifier, or Archon of Cruelty into play via Reanimate, Animate Dead, or Shallow Grave, so Force of Negation is a key proactive answer to those noncreature reanimation spells before they resolve. Consign to Memory can strip a triggered ability like Atraxa, Grand Unifier's enter-the-battlefield trigger or counter a colorless spell like Lotus Petal, and Ghost Vacuum exiles cards from their graveyard to deny reanimation targets outright. Stifle has little to hit here and Flow State is too slow against a deck that can win by turn two or three, so both are cut for interaction that actually stops their combo.