Sneak and Show is trying to resolve Show and Tell or Sneak Attack to cheat Atraxa, Grand Unifier, Emrakul, or Griselbrand into play, so the extra Force of Negation is essential to counter their enchantment or Show and Tell on the stack for free. Pithing Needle can be named on Sneak Attack to shut off its activated ability entirely, which is a clean, cheap answer to their primary combo engine. Kappa Cannoneer is far too slow in a matchup that can end on turn two or three, so trim it along with a spare Aether Spellbomb for more proactive countermagic and disruption; your own Chalice of the Void set at one or zero also disrupts their Lotus Petal and cheap cantrips.