Oneiros, God of Dreams

Indestructible
As long as your devotion to blue and black is less than seven, Oneiros isn't a creature.
Whenever a creature an opponent controls becomes tapped, exile the top card of its controller's library.
Once during each of your turns you may cast a creature card from an opponent's exile without paying its mana cost. It is a Nightmare in addition to its other types.
Oneiros gets +X/+X where X is the number of Nightmares you control.