Choose one — • Exile each creature with power greater than the number of cards in your hand. • Exile each creature with power less than the number of cards in your hand.
2019-08-23
Because Nightmare Unmaking is on the stack while it's resolving, it won't be counted among the cards in your hand.
2019-08-23
The power of creatures and the number of cards in your hand are checked only as Nightmare Unmaking resolves. Players may respond to the spell knowing the chosen mode to try to save or doom a creature.