Rule 707.9a

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 another creature enters, this creature becomes a copy of that creature, except it has 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.