What is primarily required for a successful transformation of a double-faced card?

A successful transformation of a double-faced card is primarily dependent on specific conditions being met through spells or abilities. In the game of Magic: The Gathering, double-faced cards have the ability to transform into their other face under specific circumstances laid out by their text. These conditions usually involve certain game events, such as the card being cast or being triggered by an effect.

For instance, a double-faced creature like a werewolf might transform during a specific phase of the game, often tied to whether a player has cast a spell during their last turn or if a particular environment is met. This transformation is not a generic action like sacrificing the card or attaching it to another creature; it’s contingent upon meeting the circumstances described in the card's text.

Even though other options suggest actions related to gameplay, only the option focusing on the requirement of magic spells or abilities aligns with the game's rules governing how double-faced cards function and transform. Understanding this mechanism is vital to utilizing double-faced cards effectively in various deck strategies.