Historical Rules · 5 October 2018
Rule 706.9a
Official source text from the 5 October 2018 Rules release
Some copy effects cause the copy to gain an ability as part of the copying process. This ability becomes part of the copiable values for the copy, along with any other abilities that were copied. Example: Quirion Elves enters the battlefield and an Unstable Shapeshifter copies it. The copiable values of the Shapeshifter now match those of the Elves, except that the Shapeshifter also has the ability “Whenever a creature enters the battlefield, Unstable Shapeshifter becomes a copy of that creature and gains this ability.” Then a Clone enters the battlefield as a copy of the Unstable Shapeshifter. The Clone copies the new copiable values of the Shapeshifter, including the ability that the Shapeshifter gave itself when it copied the Elves.