Living End suspends its namesake spell to reanimate its whole graveyard of creatures like Shardless Agent and Waker of Waves at once, so Rest in Peace is a devastating answer that stops the sacrifice-and-return engine from functioning entirely by exiling everything. Mystical Dispute cheaply counters their blue interaction like Force of Negation or Subtlety's evoke while also helping counter their cascade spells like Shardless Agent. Cut card selection and Prismatic Ending since neither interacts with the suspended Living End trigger itself, and Rest in Peace is a much more proactive answer to the deck's core plan. Keep counterspells like Counterspell in to catch Living End itself before it resolves.