Mask of Anonymity

{3}: Put a creature card from your hand onto the battlefield face down. (It is a 2/2 colorless creature with no name, mana cost, creature types, or abilities.)
You may turn face down creatures you control face up by paying their mana costs if they are creature cards.
"Who am I? I am everyone, and I am no one. Until my mask is removed, you shall never truly know."