Face-Down

Stratus Dancer card art

I conclude self-proclaimed 'rules month' with a post on face-down cards. The forthcoming set, Murders at Karlov Manor, feature a keyword relevant to the topic.

Face-down cards were introduced with the 'morph' mechanic in Onslaught (2002). 'Megamorph' (Dragons of Tarkir, 2015) was similar, and now we have 'disguise' with Murders at Karlov Manor. We'll start with morph. Selections from the official rules, section 702.37:

“Morph [cost]” means “You may cast this card as a 2/2 face-down creature with no text, no name, no subtypes, and no mana cost by paying {3} rather than paying its mana cost.” 

You do *not* show the card to your opponent(s) when doing this; it is taken on trust (only cards with a morph ability can be cast face-down; rule 702.37d). So morph cards give you a choice: cast it face-up for its normal casting cost, or pay {3} and cast it face-down as a 2/2 generic creature. At a later time, whenever you have priority, you may pay the face-down card's morph cost (which is stated on the card) to turn it face-up (rule 702.37e). From the same rule:

Turning face-up "is a special action; it doesn’t use the stack." 

"Any abilities relating to the permanent entering the battlefield don’t trigger when it’s turned face up and don’t have any effect, because the permanent has already entered the battlefield." 

Megamorph is the same, but the creature gains a +1/+1 counter when it is turned face-up (see 702.37b). 

Disguise (the latest keyword) is the same, but the creature as 'ward 2' while face-down.

Four examples below on the varying costs and benefits of turning cards face-up. The general idea is that casting it face-down first will grant a later benefit.

Section 708 of the rules covers face-down spells and permanents. A lot of that section deals with the characteristics of face-down permanents (and its interactions with spells that may copy the card/etc.). Relevant portions:

708.2. Face-down spells and face-down permanents have no characteristics other than those listed by the ability or rules that allowed the spell or permanent to be face down. Any listed characteristics are the copiable values of that object’s characteristics. 

708.2a [shortened] If a face-up permanent is turned face down by a spell or ability that doesn’t list any characteristics for that object, it becomes a 2/2 face-down creature with no text, no name, no subtypes, and no mana cost.

708.3. 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). 

708.4. 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. 

708.6 [shortened]. 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.  

708.11. 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.

It is pretty straightforward, but warranted explanation, as it is one aspect of the game that can trip up the novice.