Characteristic-defining ability

A characteristic-defining ability is a kind of static ability that conveys information about an object's characteristics that would normally be found elsewhere on that object (such as in its mana cost, type line, or power/toughness box).

Characteristic-defining abilities are noteworthy because they are active at all times, even while not in play or outside of the game.

Characteristic-defining keywords are:

• Changeling — grants every creature type (e.g. Avian Changeling).
• Devoid — makes an object colorless, despite the presence of colored mana in the mana cost (e.g. Touch of the Void).

Other examples are:

• Transguild Courier is all colors.
• Veteran Adventurer is also a Cleric, Rogue, Warrior, and Wizard.
• Boneyard Mycodrax's power and toughness are each equal to the number of other creature cards in your graveyard.

Rules

From the glossary of the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

Characteristic-Defining Ability

A kind of static ability that conveys information about an object’s characteristics that would normally be found elsewhere on that object (such as in its mana cost, type line, or power/toughness box). See rule 604.3.

From the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

• 604.3. Some static abilities are characteristic-defining abilities. A characteristic-defining ability conveys information about an object’s characteristics that would normally be found elsewhere on that object (such as in its mana cost, type line, or power/toughness box). Characteristic-defining abilities can add to or override information found elsewhere on that object. Characteristic-defining abilities function in all zones. They also function outside the game and before the game begins.
  • 604.3a A static ability is a characteristic-defining ability if it meets the following criteria: (1) It defines an object’s colors, subtypes, power, or toughness; (2) it is printed on the card it affects, it was granted to the token it affects by the effect that created the token, or it was acquired by the object it affects as the result of a copy effect or text-changing effect; (3) it does not directly affect the characteristics of any other objects; (4) it is not an ability that an object grants to itself; and (5) it does not set the values of such characteristics only if certain conditions are met.

From the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

• 707.9d When applying a copy effect that doesn’t copy a certain characteristic, retains one or more original values for a certain characteristic, or provides a specific set of values for a certain characteristic, any characteristic-defining ability (see rule 604.3) of the object being copied that defines that characteristic is not copied. If that characteristic is color, any color indicator (see rule 204) of that object is also not copied. This rule does not apply to copy effects with exceptions that state the object is a certain card type, supertype, and/or subtype “in addition to its other types.” In those cases, any characteristic-defining ability that defines card type, supertype, and/or subtype is copied.

  Example: Quicksilver Gargantuan is a creature that reads, “You may have Quicksilver Gargantuan enter the battlefield as a copy of any creature on the battlefield, except it’s 7/7.” Quicksilver Gargantuan enters the battlefield as a copy of Tarmogoyf, which has a characteristic-defining ability that defines its power and toughness. Quicksilver Gargantuan does not have that ability. It will be 7/7.

  Example: Glasspool Mimic is a creature that reads “You may have Glasspool Mimic enter the battlefield as a copy of a creature you control, except it’s a Shapeshifter Rogue in addition to its other types.” Glasspool Mimic enters the battlefield as a copy of a creature with changeling. Glasspool Mimic will have changeling and will have all creature types.