Jeskai Ephemerate is a value/control deck with Mulldrifter, Archaeomancer, and Murmuring Mystic rather than a fast combat clock, so combat Fog effects are less necessary and can be trimmed for interaction. Hydroblast destroys their red permanents or counters their red spells like Skred, giving you proactive answers against a deck that otherwise out-grinds you with card advantage. Their own Counterspell and Dispel suite means you should sequence your card draw (Lembas, Eviscerator's Insight) carefully to bait counters. Keep Crypt Rats and Darkness since their early creatures (Augur of Bolas, Faerie-adjacent bodies) are small and vulnerable to a sweep.