This is a cascade mirror where their win condition depends entirely on resolving Living End with a full graveyard — Endurance answers this cleanly by exiling their graveyard at instant speed in response to Living End, leaving them with a board of nothing. Mystical Dispute is the best counter in the mirror since nearly every relevant spell is blue (Force of Negation, Violent Outburst, Shardless Agent), and Tishana's Tidebinder can counter cascade triggered abilities on the stack, letting you neutralize their Shardless Agent or Violent Outburst cascade without needing a hard counter. Brotherhood's End is too slow and does too little against a board of cycled fatties, and Fire/Ice lacks impact in a matchup decided by counter wars and graveyard interaction rather than incremental damage. Leave up Endurance on their end step whenever possible — don't tap out into their Violent Outburst window.