UBG Reanimator relies entirely on the graveyard via Faithless Looting, Reanimate, Animate Dead, and Shallow Grave to cheat in Atraxa, Griselbrand, or Archon of Cruelty, making Rest in Peace a devastating answer that exiles their graveyard and prevents any reanimation. Force of Negation lets us proactively counter their Reanimate, Animate Dead, or Shallow Grave for free, which is crucial against their hand-disruption-heavy, fast combo draws. Back to Basics is weak here since their manabase runs plenty of basics (Swamp) alongside fetches they'll crack before locking lands matters. Gandalf is too slow and vulnerable to their discard and ritual-fueled combo turns, so it comes out for more proactive answers.