Transform

Transform is a keyword action introduced in Innistrad and means to turn a double-faced card on the back side, changing the card face that is visible. 
==Description==
Each double-faced card has a front face. This face is the default; double-faced permanents start on the battlefield with this face upwards. If an ability instructs you to transform the permanent, you turn it over so its other face is up. Whichever face is up at the time tells you what that permanent is and what it can do.
==History==
The mechanic was developed to properly depict Werewolves: creatures on both sides in , with a day-night mechanic, in expansions set on Innistrad. However, the space available for transforming (such as depicting journeys to new lands, story magic coming to life, defenders of a plane under attack, creating new tools from defunct artifacts) made it so that simple creature-creature transformations became rarer in relative.
Dark Ascension introduced some different transforming cards; the first transforming artifacts, the first creature that returned from death transformed, and the first creature that transforms into an aura.
Magic Origins has five legendary creatures who are exiled and then returned transformed (into planeswalkers) from the exile zone.
Shadows over Innistrad saw a sorcery that transforms from the graveyard into a creature, an Aura that returns from the graveyard that transforms into a creature, an artifact that transforms upon death from a creature to an equipment, and a land that transforms into a creature.
Ixalan block had all artifacts or enchantments that transformed into lands.
Core Set 2019 has another creature-into-planeswalker flip card and follows the Magic Origins format.
Innistrad: Midnight Hunt introduced the first mechanics that integrate transform into their rules text, Disturb and Daybound and Nightbound. It also features a creature that transforms into an artifact and the first card to transform through a replacement effect rather than a triggered or activated ability. Innistrad: Crimson Vow featured two enchantments that transform into other enchantments.
Kamigawa: Neon Dynasty introduced transforming Sagas. All of them exile themselves on their third chapter and return, transforming from Sagas to enchantment creatures.
March of the Machine introduced the new card type Battle with the subtype Siege that are exclusively double-faced cards. Battles have a number of counters that represent the damage it can sustain before being defeated. All Battles are currently Sieges, which give your opponent means to defend them and they are exiled and cast transformed when defeated.
==="Transformation matters"===
The use of TDFCs representing the Phyrexians in March of the Machine allowed R&D to use "transformation matters" as a theme that ran through the Phyrexian side of the conflict, but also played well with the Battles.
==Rules==
==Rulings==
* "Double-faced" used to refer only to the physical card. With March of the Machine double-faced tokens were introduced. Transforming double-faced tokens can transform, including tokens that are copies of transforming double-faced permanents. 
* Each face of a double-faced card has its own name, types, subtypes, power and toughness, abilities, and so on. While a double-faced card is not on the battlefield, consider only the characteristics of its front face. While a double-faced card is on the battlefield, consider only the characteristics of the face that's currently up. The other set of characteristics is ignored. 
*As an exception to the previous ruling, the mana value of a transforming double-faced permanent’s back face is calculated as though it had the mana cost of its front face. However, a copy of a transforming double-faced permanent with its back face up will have no mana cost, and a mana value of 0.
* A transforming double-faced card enters the battlefield with the front face up unless it is stated that the card enters the battlefield transformed.
* The back face of a transforming double-faced card can't be cast.
* Transforming a permanent doesn't affect any Auras or Equipment attached to that permanent. Similarly, any counters on the permanent will remain on that permanent after it transforms.
* Damage marked on a double-faced permanent will stay marked on that permanent after it transforms.
==See also==
* Morph
* Meld
* Flip cards
* Convert
==References==