What occurs when a copy effect copies an object with a power/toughness characteristic-defining ability (CDA)?

When a copy effect creates a copy of an object with a characteristic-defining ability (CDA) that influences its power and toughness, the correct result is that the copy sets its own power and toughness based on that CDA. This is because CDAs define how the object's characteristics work, meaning that any copy of the object will reflect the current defined values dictated by that ability.

For example, if a creature has a CDA that states its power and toughness are determined by a certain parameter, the copy effect will use that parameter to establish the new copy's power and toughness. Thus, the copy does not merely mirror the original's statistics; instead, it establishes its own based on the defining characteristics established in the game.

This understanding aligns with the rules surrounding characteristic-defining abilities in Magic: The Gathering, where the definitions set by a CDA are the basis on which copies that include those characteristics are created.