Doomsday is a fast combo deck that assembles a Doomsday pile to win through Thassa's Oracle or Jace, Wielder of Mysteries, and it's a pure combo race with heavy countermagic from both sides. Pyroblast is your best tool here — it counters Force of Will, Daze, Flusterstorm, and Doomsday itself, and having a free piece of countermagic at instant speed is invaluable when you're trying to resolve Show and Tell through multiple layers of interaction. Consign to Memory answers Thassa's Oracle on the stack and exile-effects are important here since they can't be pitched to Force of Will. Hexing Squelcher applies clock pressure and taxes their spell-casting, which matters because Doomsday often needs very specific mana timing to execute the full combo. Sneak Attack is too slow in a matchup where they can win on turn one or two, and Prismari Charm and Spell Pierce are outclassed by your new additions in the counterspell battle.