Leyline of the Unknown

If Leyline of the Unknown is in your opening
hand, you may begin the game with it on the
battlefield.
Creatures enter the battlefield face down as a
2/2 creature and can be turned face up any
time for it's mana cost.
Reality may yet only be reliable perception. Your
world is never seen by anyone else; who is to say any
of this has ever been real?