Jeskai Ephemerate plays a reasonable amount of red via Skred, so Blue Elemental Blast is a strong upgrade to destroy or counter it along with any other red permanent or spell they present. The second Dispel helps you win the counter-war over their own Counterspell and Dispel while protecting your key threats and answers. Cryoshatter is a weak cut candidate since -5/-0 does nothing to Murmuring Mystic or Archaeomancer's ability to survive, as it only reduces power, and their Ephemerate-based blink engine means removal that doesn't remove the creature from the game is less valuable. Prioritize countering their Ephemerate targets like Mulldrifter and Murmuring Mystic on the stack, since letting their blink engine resolve generates significant card and board advantage.