Is it to soon for theories about S3 idk but here we go!
So my theory is Marcy gets possessed by the Night. But then at the mid season finale or actual finale Anne and Sasha free her. So then the Night decides to possess king Andrias. So he can have another vessel and he can concure and rule. The Night could very well be using Andrias the same way Andrias was using Marcy. Feeding into Andrias vulnerability to get what he wants. It would make for an interesting parallel. I don't think any of us would mind Andrias being back stabbed though lol.
Or maybe Andrias and the Night fuse?