Duress is excellent proactive disruption, stripping their Show and Tell or a protective counterspell like Force of Will before they can deploy Omniscience or Emrakul, the Aeons Torn. Void Mirror shuts down free spells cast off Omniscience as well as Force of Will cast for its alternative cost, since no colored mana is spent to cast them. Barrowgoyf is a resilient clock that punishes them if they stumble. Malevolent Rumble and Witherbloom Charm are too slow against a deck that can win as early as turn two or three off Show and Tell into Omniscience, and Pithing Needle is better replaced by more proactive disruption here.