Double-faced Cards were first introduced in Magic with the set Innistrad and represent a radical change for the card back.     Until their release, no legal card could have a different print on the back than the regular Magic card back. However, double-faced cards have a regular card frame on each side. In Innistrad there are 2 white, 3 blue, 2 black, 6 red and 7 green double-faced cards. In Dark Ascension there are 1 white, 1 blue, 2 black, 3 red, 3 green, 1 multicolored and 2 artifact double-faced cards.
From the Comprehensive Rules (Innistrad)
- 711. Double-Faced Cards
- 711.1. A double-faced card has a Magic card face on each side rather than a Magic card face on one side and a Magic card back on the other. Each face may have abilities that allow the permanent to "transform," or turn over to its other face. Tokens and cards with a Magic card back can't transform. (See rule 701.25, "Transform.")
- 711.1a A double-faced card's front face is indicated by the sun symbol in its upper left corner.
- 711.1b A double-faced card's back face is indicated by the moon symbol in its upper left corner.
- 711.1c While a double-faced card is in a public zone, each player may look at both faces. In other zones, each player that is allowed to look at a double-faced card may look at both faces.
- 711.1d If the back face of a double-sided card is a creature, the front face of that card will have the back face's power and toughness printed in italicized gray text in the lower right of its text box. This is reminder text and has no effect on game play.
- 711.2. Each face of a double-faced card has its own set of characteristics.
- 711.2a In every zone other than the battlefield, and also on the battlefield with its front face up, a double-faced card has only the characteristics of its front face.
- 711.2b While a double-faced permanent's back face is up, it has only the characteristics of its back face. The back face doesn't have a mana cost; it has the colors in its color indicator (see rule 202.2e), if any.
- 711.3. Except for determining whether or not a permanent can transform, a spell, ability, or rule that needs information about a double-faced permanent sees only the information given by the face that's currently up.
Example: A Clone enters the battlefield as a copy of Wildblood Pack (the back face of a double-faced card). The Clone will be a copy of Wildblood Pack. Because the Clone is itself not a double-faced card, it can't transform.
Example: A player casts Cytoshape, causing a Kruin Outlaw (the front face of a double-faced card) to become a copy of Elite Vanguard (a 2/1 Human Soldier creature) until the end of turn. The player then casts Moonmist, which reads, in part, "Transform all Humans." Because the copy of Elite Vanguard is a double-faced card, it will transform. The resulting permanent will have its back face up, although it will still be a copy of Elite Vanguard that turn.
- 711.4. If a double-faced card is cast as a spell, it's put on the stack with its front face up. A double-faced card can't be cast face down. See rule 601, "Casting Spells."
- 711.5. A double-faced card enters the battlefield with its front face up unless a spell or ability puts it onto the battlefield "transformed," in which case it enters the battlefield with its back face up.
- 711.6. A double-faced permanent always has the status "face up" (see rule 110.6). Double-faced permanents can't be turned face down. If a spell or ability tries to turn a double-faced permanent face down, nothing happens.
- 711.7. When a double-faced permanent transforms, it doesn't become a new object. Any effects that applied to that permanent will continue to apply to it after it transforms.
Example: An effect gives Village Ironsmith (the front face of a double-faced card) +2/+2 until end of turn and then Village Ironsmith transforms into Ironfang. Ironfang will continue to get +2/+2 until the end of turn.
- 711.8. If an effect instructs a player to name a card, the player may name either face of a double-faced card but not both.
- 711.9. Players must ensure that double-faced cards in hidden zones are indistinguishable from other cards in the same zone. To do this, the owner of a double-faced card may use completely opaque card sleeves or substitute a checklist card. Sanctioned tournaments have additional rules for playing with double-faced cards. See rule 100.6.
- 711.9a If a checklist card is used, the double-faced card it represents must be set aside prior to the beginning of the game (see rule 103.1a) and must be available throughout the game. A checklist card can't be included in a deck unless it is representing a double-faced card.
- 711.9b The face of each checklist card is divided into sections. Each section lists the name and mana cost of each double-faced card it could represent and includes a fill-in circle. When using a checklist card, exactly one of the fill-in circles must be marked to denote which double-faced card the checklist card represents.
- 711.9c For all game purposes, a checklist card is considered to be the double-faced card it's representing. It has that double-faced card's characteristics in all zones.
- 711.9d As the checklist card enters a public zone, the checklist card should be set aside and the double-faced card used instead. If the checklist card is exiled face down, its identity should continue to be hidden using the face-down checklist card.
 Playing with double-sided cards
Double-faced cards have an icon next to the name representing a sun or a moon. The front of the card is called the day side and has a regular card frame and has the sun symbol. The night side has the moon symbol and a slightly altered frame similar to Planeshifted cards with a darker textbox and white text for the card type, name, and Power/Toughness.
Double-sided cards enter the battlefield with their day side. To switch between the two card faces, the keyword action transform is used. During transformation, all counters, Auras and Equipment stay on the card, and the card neither enters nor leaves the battlefield.
To be allowed to play with double-sided cards, the player must have opaque sleeves for all his cards through which no detail of the cards are visible. If the player has no sleeves or only non-opaque sleeves, the player may use a checklist card which are available with the sets. Checklist cards have the regular magic card back and list all double-faced cards from a set. The player must mark which double-faced card the checklist card is meant to represent on the checklist card, in a manner not visible from the the back of the card. The checklist card is shuffled into the deck while the actual double-faced card is kept outside the game.
 Double-faced card rulings
- Double-faced cards can not be turned face down with cards such as Ixidron. When a double-faced card is instructed to be turned face-down, nothing happens. Similarly, if a non-double-faced card is instructed to transform, nothing happens.
- When a double-sided card is copied, e.g. with a card like Clone, only the characteristics of the face that is currently visible upon copying are copied. Such copies can not transform either.
- If a card is not in play, the only information relevant and viewable for other cards is the day side of the card.
- The color identity of the card includes either face.
 Checklist card rulings
- It's important that the cards in your deck be indistinguishable from one another. To accomplish this with double-faced cards, you can use the checklist cards included in some Innistrad booster packs and in the Innistrad fat pack. These checklist cards have a list of all double-faced cards in the Innistrad set on one side and the typical Magic card back on the other side.
- You must have with you the actual double-faced card the checklist card is representing. The double-faced card should be kept apart from the rest of your deck. In tournaments, the double-faced card should also be kept separate from your sideboard.
- A checklist card can't be included in a deck except when it's being used to represent a double-faced card.
- You must mark exactly one fill-in circle on the checklist card to indicate which double-faced card it represents.
- You can still use card sleeves, even if you also choose to use checklist cards.
- During the game, a checklist card is considered to be the double-faced card it represents. For example, say you have a checklist card in your hand representing Tormented Pariah and an opponent casts Despise. The checklist card is a creature card, so your opponent may choose the checklist card and you would discard it.
- As soon as a checklist card enters a public zone (stack, battlefield, graveyard, or exile unless it's exiled face down), use the double-faced card and set the checklist card aside. If the double-faced card is put into a hidden zone (hand or library), use the checklist card again.
- If a double-faced card is exiled face down, keep its identity hidden by using the face-down checklist card.
- ↑ Mark Rosewater. (August 29, 2011.) "Every Two Sides Has a Story", Daily MTG, magicthegathering.com, Wizards of the Coast.
- ↑ Monty Ashley. (September 21, 2011.) "The Two Sides", Daily MTG, magicthegathering.com, Wizards of the Coast.
- ↑ Mark Rosewater. (August 05, 2013.) "Twenty Things That Were Going To Kill Magic", Daily MTG, magicthegathering.com, Wizards of the Coast.
- ↑ Wizards of the Coast. (August 28, 2011.) "Double-Faced Card Rules", Daily MTG, magicthegathering.com, Wizards of the Coast.