Sneak and Show wants to cheat Atraxa, Griselbrand, or Emrakul into play via Sneak Attack or Show and Tell, so free counterspells are your best tool to stop the enabler before the giant threat ever hits the battlefield. Force of Negation and Mindbreak Trap can counter Show and Tell or Sneak Attack for free, and Mindbreak Trap is especially strong once they chain multiple cantrips in a turn, letting you exile the key spell for {0}. Consign to Memory is live mainly against their colorless spells and triggered abilities, so it's a lower-priority include but still cheap insurance. Chalice of the Void mainboard already punishes their 0 and 1-mana suite (Lotus Petal, Brainstorm, Ponder) so it stays in unchanged.