Sneak and Show is a mirror-ish combo race built around Show and Tell and Sneak Attack cheating in Atraxa, Grand Unifier, Griselbrand, or Emrakul, the Aeons Torn, so the game comes down to who resolves their payoff first and protects it with Force of Will. Faerie Macabre gives you a proactive way to discard it and exile up to two cards from a graveyard, which can strip a delve piece or graveyard resource if the game goes long, while still functioning as a flying blocker in a pinch. Omniscience is replaced since it's too slow and mana-hungry in a race where both decks are trying to win quickly off a single Show and Tell or Sneak Attack activation.