Jeskai Ephemerate is blue-heavy with Counterspell, Mulldrifter, Archaeomancer, and Murmuring Mystic, making Red Elemental Blast a strong tool to counter their Counterspell or destroy a resolved blue permanent. Breath Weapon's 2 damage to each non-Dragon creature kills their 1/1 Bird tokens from Murmuring Mystic, as well as Archaeomancer (1/2) and Mulldrifter (2/2), so it can two-for-one if they overextend. It won't kill Augur of Bolas (1/3) or Murmuring Mystic (1/5), and it also hits our own small creatures, so time it carefully. Alms of the Vein and two Rakdos Carnarium come out since the lifegain and tempo loss are too slow against their grindy card advantage plan; we need to be proactive with burn to the face and efficient removal before they out-value us with Mulldrifter and Archaeomancer loops.