Nyx, The Forgotten Death

Nyx’s power and toughness are each equal to the total number of cards among all graveyards and in exile.
Whenever Nyx, The Forgotten Death attacks:
• Each opponent mills 4 cards
• Exile a random nonland card from each opponent’s graveyard. You may cast one of those cards without paying its mana cost this turn.

"You pray for death. You beg for release.
I grant neither."