What is the duration of the doppelganger's Shapechanger ability, which lets them "polymorph" into a humanoid they have seen?
It isn't clear to me from its description in the Monster Manual.
Is the doppelganger's shapeshifting ability is just that they are able to cast a successful polymorph spell automatically, and therefore it's subject to the duration of that spell? Or can they can remain in whatever form they choose for as long as they like?