If Volrath's Shapeshifter is a copy of say a Lurrus of the Dream-Den (or Serra Paragon, or Muldrotha, the Gravetide) and then you cast something from the graveyard with the effect and it then becomes a copy of something else, just to switch back to the former Lurrus, can you then cast another card ? As the instance of the effect is a "new" one ?
Note that Volrath's Shapeshifter technically doesn't become a "copy" of anything, but rather has the full text of a certain card plus additional text.
I want to point out that the answer to your question may hinge on the answer to the following question: If a permanent has the full text of a card in a graveyard, then instead has the full text of a second card for a time, then goes back to having the first card's "full text", are the abilities at the beginning and end of this scenario the same "instances"? Observe here that the first card hasn't moved out of the graveyard in this scenario.
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I want to point out that the answer to your question may hinge on the answer to the following question: If a permanent has the full text of a card in a graveyard, then instead has the full text of a second card for a time, then goes back to having the first card's "full text", are the abilities at the beginning and end of this scenario the same "instances"? Observe here that the first card hasn't moved out of the graveyard in this scenario.
See also:
- https://www.reddit.com/r/mtgrules/comments/xt93ef/question_about_ratchet_field_medic_ratchet_rescue/ (transforming and transforming back)
- https://www.reddit.com/r/mtgrules/comments/r0snor/hasnt_been_chosen_for_transformedcopied_cards/ (same)
- https://www.mtgsalvation.com/forums/magic-fundamentals/magic-rulings/802624-realm-razor-and-sudden-spoiling (losing abilities for a time)
- https://twitter.com/PeteroUPC/status/1463323874632908803