707.1 Some cards allow spells and permanents to be face down.
707.2a If a face-up permanent is turned face down by a spell or ability, it becomes a 2/2 face-down creature with no text, no name, no subtypes, and no mana cost. A permanent that enters the battlefield face down that wasn't cast as a face-down spell also has these characteristics. These values are the copiable values of that object's characteristics.
707.3 Objects that are put onto the battlefield face down are turned face down before they enter the battlefield, so the permanent's enters-the-battlefield abilities won't trigger (if triggered) or have any effect (if static).
707.4 Objects that are cast face down are turned face down before they are put onto the stack, so effects that care about the characteristics of a spell will see only the face-down spell's characteristics. Any effects or prohibitions that would apply to casting an object with these characteristics (and not the face-up object's characteristics) are applied to casting this object. The permanent the spell becomes will be a face-down permanent.
707.5 At any time, you may look at a face-down spell you control on the stack or a face-down permanent you control (even if it's phased out). You can't look at face-down cards in any other zone or face-down spells or permanents controlled by another player.
707.6 If you control multiple face-down spells or face-down permanents, you must ensure at all times that your face-down spells and permanents can be easily differentiated from each other. This includes, but is not limited to, knowing what ability or rules caused the permanents to be face down, the order spells were cast, the order that face-down permanents entered the battlefield, which creature(s) attacked last turn, and any other differences between face-down spells or permanents. Common methods for distinguishing between face-down objects include using counters or dice to mark the different objects, or clearly placing those objects in order on the table.
707.7 The ability or rules that allow a permanent to be face down may also allow the permanent's controller to turn it face up. Spells normally can't be turned face up.
707.8 As a face-down permanent is turned face up, its copiable values revert to its normal copiable values. Any effects that have been applied to the face-down permanent still apply to the face-up permanent. Any abilities relating to the permanent entering the battlefield don't trigger and don't have any effect, because the permanent has already entered the battlefield.
707.9 If a face-down permanent moves from the battlefield to any other zone, its owner must reveal it to all players as he or she moves it. If a face-down spell moves from the stack to any zone other than the battlefield, its owner must reveal it to all players as he or she moves it. If a player leaves the game, all face-down permanents and spells owned by that player must be revealed to all players. At the end of each game, all face-down permanents and spells must be revealed to all players.
707.10 If a face-down permanent becomes a copy of another permanent, its copiable values become the copiable values of that permanent, as modified by its face-down status. Its characteristics therefore remain the same: the characteristics listed by the ability or rules that allowed it to be turned face down. However, if it is turned face up, its copiable values become the values it copied from the other permanent. See rule 706.3.
707.11 If a face-down permanent would have an "As [this permanent] is turned face up . . ." ability after it's turned face up, that ability is applied while that permanent is being turned face up, not afterward.