Avatar of Nyx, Fate Incarnate

Avatar of Nyx, Fate Incarnate has Hexproof if you have five or less Arcana cards in exile.
If Avatar of Nyx would leave the battlefield, exile Avatar of Nyx instead. If you do, return it to the battlefield and exile the top card of the Arcana deck. You may cast the exiled card without paying its mana cost. (The Arcana Deck is a seperate deck that is shuffled at the beginning of the game.)