Rulings

• 2018-07-13
  If another permanent that isn't a double-faced card (such as Mirror Image) becomes a copy of Nicol Bolas, the Ravager, activating the ability to exile it and return it transformed will only exile it. It won't return to the battlefield at all.
• 2018-07-13
  A double-faced card enters the battlefield with its front face up by default, unless a spell or ability instructs you to put it onto the battlefield transformed, in which case it enters with its back face up. The back face of a double-faced card can't be played.
• 2018-07-13
  While a double-faced card isn't on the battlefield, consider only the characteristics of its front face. For example, Nicol Bolas has the characteristics of its creature face in the graveyard, even if it was a planeswalker on the battlefield before it was put into the graveyard.
• 2018-07-13
  Each face of a double-faced card has its own set of characteristics: name, types, subtypes, abilities, and so on. While a double-faced card is on the battlefield, consider only the characteristics of the face that's currently up. The other set of characteristics is ignored.
• 2018-07-13
  If Nicol Bolas leaves the battlefield after his creature face's activated ability has been activated but before it resolves, the card remains in whichever zone it moves to. It won't be exiled or return transformed.
• 2018-07-13
  When Nicol Bolas's enters-the-battlefield triggered ability resolves, first the next opponent in turn order (or, if it's an opponent's turn, that opponent) chooses a card in their hand without revealing it, then each other opponent in turn order does the same. Then all the chosen cards are discarded at the same time.