Historical Rules · 1 October 2009
Rule 207.2b
Official source text from the 1 October 2009 Rules release
The card may have a static ability that creates a replacement effect that sets the creature's power and toughness to one of a number of specific choices as it enters the battlefield or is turned face up. (See rule 614, "Replacement Effects.") Such an ability is worded "As [this creature] enters the battlefield . . . ," "As [this creature] is turned face up . . . ," or "[This creature] enters the battlefield as . . ." and lists two or more specific power and toughness values (and may also list additional characteristics). The characteristics chosen with these effects affect the creature's copiable values; see rule 706.2. While the card isn't on the battlefield, its power and toughness are each considered to be 0.