Hydroblast is live against their red cards like Skred, countering the spell before it can deal damage, and it can also destroy a resolved red permanent, giving you cheap, flexible interaction. Dispel protects your key spells from their Counterspell and Dispel, and can stop their Ephemerate at instant speed to blank a value trigger like Archaeomancer or Mulldrifter's re-entry. This matchup rewards efficient interaction over grindy value, since Jeskai Ephemerate wants to out-value you with recurring ETBs, so prioritize disruption that keeps them off their engine.