Doomsday is a pure combo mirror where the winner is usually whoever protects their combo turn best, since both decks race to assemble a kill with Brainstorm, Ponder, and free countermagic like Force of Will. Flusterstorm and Consign to Memory (which counters colorless spells like Lion's Eye Diamond or Lotus Petal, as well as Thassa's Oracle's win trigger) give us more ways to fight through their protection on our combo turn, while Lavinia, Azorius Renegade slows their setup by stopping free spells and fast mana. We trim Shuko and Cabal Therapy since neither helps in a race defined by resolving a combo piece through countermagic, and cut Orim's Chant since our own hard counters are more reliably impactful here.