This opponent self-mills constantly, so exiling their graveyard with Nihil Spellbomb actually hurts Tolarian Terror and Cryptic Serpent's cost reduction and can be timed well, but it's still a reactive one-shot effect that doesn't stop the engine outright once they've dumped cards; swap toward proactive disruption instead. Duress is the best tool, stripping Counterspell or a key cantrip before they can protect a cheap Tolarian Terror/Cryptic Serpent. Red Elemental Blast hits almost everything they play (Counterspell, Brainstorm, Delver, Terror, Serpent), and its destroy mode kills any blue permanent regardless of size, though Tolarian Terror's ward {2} means we have to pay extra to target it. Even so, we'd rather not cut further engine pieces for it this round; a small Duress-only swap keeps our core intact while directly attacking their permission and mill-cantrip plan. Keep everything else, including Cast Down, as removal for Tolarian Terror and Cryptic Serpent once they resolve.