The Comprehensive Rules don't really explain ability instantiation and yet the rules framework relies on this concept to make things like activation limitations function.

 

It seems sensible that ability instantiation should be tied to time stamps, given that continuous effects often give abilities directly or indirectly by giving rules text through text-changing or copy effects. Additionally, objects are already given a time stamp as they enter a zone.  

 

Of course, we can't rely solely on time stamps because there are continuous effects from static abilities and that may grant rules text or abilities to objects and such effects aren't typically "locked in". For example: Necrotic Ooze with two Wall of Roots in the yard grant two distinct instances of its activated ability and yet the time stamp of the effect granting those abilities is the same, so we need to use something else to differentiate them and clearly the thing that differentiates them is the fact that the abilities are pulled from two different objects. If a Wall of Roots leaves the graveyard, that ability instance is no longer added to Ooze because that object no longer exists and if later that same Wall of Roots ends up in the graveyard again, Ooze will have a new instance because there's a new object in the yard.

 

If I activate Wall of Roots, then drop Humility (removing the ability instance), and still same turn Humility is removed, the ability instance present is still the same one so the activation limitation is still in place. We can verify this by the time stamp of Wall of Roots, same object, same rules text, same derived ability.

 

Now, what if I activate Wall of Roots, then later same turn someone Mirrorweaves another one on the field, can I activate it now?
The answer is yes. We can derive that the object's rules text was added at a different time stamp (as Mirrorweave resolved and created the copy effect which can be loosely derived from the second part of CR613.7a) and therefore the ability derived from it is also a new instance. Further, the rules text was clearly pulled from a different object. Once Mirrorweave expires in the cleanup step, if players were to get priority then, could it be activated again? No, we're back to the ability instance it had before Mirrorweave was applied.

 

Now, what if I have two Nightveil Specters and both of the Specters have cards exiled. I also have three 1/1 bat tokens. I cast Mirrorweave targeting Specter A, making Specter B and the bats copies of Specter A and giving them their own instances of rules text from Specter A. Specter A is unaffected and can still access its exiled cards, but can Specter B? No, the ability instances it has now are linked to each other so can't be linked to the abilities overwritten by the copy effect (which are the ability instances linked to the cards in exile). What about once Mirrorweave ends? Any cards Specter B had exiled prior to Mirrorweave being applied are back on the table because the ability instances that exiled them are back. However, if Specter B had exiled a card while a copy of Specter A, that card is now inaccessible.

 

Let's look at Volrath's Shapeshifter. If Wall of Roots is the top card of the yard, Shapeshifter pulls its rules text (and name and typeline). If I activate the ability on Shapeshifter, derived from the rules text pulled from the Wall of Roots object in the yard, what stops me from activating it again after the next change in game state. Clearly, it's the same ability instance, but what makes it so. Well, presumably, same time stamp for the ability based on effect time stamp and because it is an effect from a static ability, it's pulled from same object. 
Now, if a second Wall of Roots drops overtop of the first in the yard. Shapeshifter's effect still has the same time stamp, but it is pulling from a different object, clearly this means it has a new ability instance because the object is distinct (not unlike Necrotic Ooze). If I activate the ability, can I activate it again after the next game state change? No, same time stamp, same object pulled from, same ability instance derived. What if Wall of Roots B leaves the graveyard and puts Wall of Roots A back on top, all still on the same turn, can I activate the ability again? No. Shapeshifter has the same ability instance it had before Wall of Roots B entered because the continuous effect applying the rules text to it has the same time stamp and is pulled from the same object. It's essentially the same as the Nightveil Specter situation.

 

Why? CR207.1 and CR707.2a

207.1. The text box is printed on the lower half of the card. It usually contains rules text defining the card's abilities.
707.2a. A copy acquires the color of the object it's copying because that value is derived from its mana cost or color indicator. A copy acquires the abilities of the object it's copying because those values are derived from its rules text. A copy doesn't wind up with two values of each ability (that is, it doesn't copy the object's abilities and its rules text, then have that rules text define a new set of abilities).

 

Clearly, the abilities are distinct instantiations based on the rules text of the source object and the time stamp. In the case of Nightveil Specter, the link was maintained because the abilities were derived from the same rules text it has inherently (ie. it is itself the source object the abilities are pulled from). In the case of Shapeshifter, the same is true, the rules text is once again pulled from Wall of Roots A with the same effect time stamp and same source object so must be the same instance of the ability.

 

The counter argument seems to be that the rules text on Shapeshifter is updated each time the card in the yard changes, but that view doesn't hold any merit.
While I agree that the rules text of Shapshifter updates as the game state changes (as stated in CR613.1 and CR613.5), it seems inconsistent that it only updates in game states where the top card in the yard changes. The only way this works consistently is if instantiation tracks firstly time stamp (either of the object the rules text is on or the effect that puts that rules text there) and secondarily the source object that it pulls the ability or rules text from. As such, given that the time stamp and source object pulled from are the same, Volrath's Shapeshifter must have the same ability instance it had before Wall of Roots B dropped on top of Wall of Roots A that it does after Wall of Roots B leaves the yard, the same as how Nightveil Specter preserves its link.

 

Edited Todd Bussey (Yesterday 01:29:22 PM)