Sultai Aluren wants to resolve Show and Tell to put Atraxa, Grand Unifier or Acererak the Archlich onto the battlefield, or to resolve Aluren to free-cast creatures with mana value 3 or less (Acererak included), and our sideboard plan pressures both routes. Containment Priest is the most important card here against Show and Tell, because a nontoken creature that enters without being cast is exiled instead, so Atraxa or Acererak put in that way never stays. Priest does not stop Aluren, since creatures it free-casts are still cast, and it does nothing against creatures that are simply cast. It is a strong answer to Show and Tell but not a full lock. Note that it also exiles our own creatures that enter uncast, such as those put in with Aether Vial, so use Vial carefully while Priest is on the battlefield. Deafening Silence restricts each player to one noncreature spell per turn, which slows their setup since they rely on Aluren, Show and Tell, and cantrips like Ponder, Brainstorm and Stock Up. Flickerwisp and Pre-War Formalwear are cut as they do little against giant top-end threats or a combo plan.