In Curse of Strahd, my cleric cast Banishment on the (possible spoiler):
At the end of Banishment's duration, will the creature return? I don't know what plane it's native to. Our DM seemed unsure, himself. Our party has reason to believe that this creature is:
a silver dragon that was turned in to a shadow dragon by Strahd.
I don't have any confirmation, but I believe that the creature actually is: