Mastery of the Unseen

You must ensure that your face-down spells and permanents can easily be differentiated from each other. You're not allowed to mix up the cards that represent them on the battlefield in order to confuse other players. The order they entered the battlefield should remain clear. Common methods for indicating this include using markers or dice, or simply placing them in order on the battlefield. You must also track how each became face down (manifested, cast face down using the morph ability, and so on).

Turning a permanent face up or face down doesn't change whether that permanent is tapped or untapped.

Because face-down creatures don't have names, they can't have the same name as any other creature, even another face-down creature.