This is a Game Rule Violation, and in this case Nat can’t verify that Andy’s use of the morph ability was legal. Until recently, this would have resulted in a game loss for Andy. However, there was a point in time when Nat had the opportunity to verify the legality of the play, which was when he cast the spell that bounced the mystic. As such, the penalty is not upgraded. Andy receives a warning for Game Rule Violation. As an additional remedy, we also ask Andy to reveal the Rattleclaw Mystic to Nat.

One thing to note here is that we’re choosing to trust Andy about what card in his hand was just returned to it. A few of your responses alluded to a phrase we sometimes use when you stated that the mystic is no longer ‘uniquely identifiable’ now that it’s in Andy’s hand. While that is true, and we can’t know with 100% certainty that the mystic is the correct card, it’s okay to trust players in this sort of situation. If you don’t believe the player or you get the inkling that he may be deceiving you based on your format knowledge, feel free to investigate. However, the additional remedy for the solution includes a reveal and we’d be remiss if we didn’t do that whenever possible.