Sphinx's Decree
Oracle Text
Each opponent can't cast instant or sorcery spells during that player's next turn.
Card Rulings
1/19/2018 If multiple effects say that an opponent can’t cast instant or sorcery spells during that player’s next turn, they all apply to the same turn.
Are there a bunch of Modern or Eternal decks that rely on casting sorcery spells as quickly as possible? I am only coming up with storm and a good storm deck wouldn't even try to make their big move if you telegraph this spell (and you kind of have to, what with it being a sorcery).
Really, what is this card?