Containment Priest is the single best sideboard card available: Show and Tell and Sneak Attack both put creatures onto the battlefield without casting them, so Containment Priest exiles Emrakul, the Aeons Torn, Atraxa, Grand Unifier, or Griselbrand the moment they try to cheat them in. Witch Enchanter's removal trigger has no good targets since they run essentially no artifacts or enchantments besides Omniscience, which is rarely online before we win or lose. Keep Chalice of the Void at zero or one to disrupt Lotus Petal, Brainstorm, and Ponder, and Archon of Emeria to limit them to one spell a turn.