Grixis Reanimator can bring back Archon of Cruelty or Atraxa, Grand Unifier for a huge tempo swing via Unearth or Persist, and their sideboard leans on Consign to Memory and Mystical Dispute of their own to protect that plan. Bring in your own Mystical Dispute for {U} to strip away their counter magic, and Teferi, Time Raveler to shut off their instant-speed disruption entirely on your turn, letting your suspended Living End resolve cleanly. This is a race where both decks are trying to reanimate or cheat threats into play, so prioritize protecting your own game plan over trying to interact with theirs.