Plot: Threat from the North vs The First Snow of Winter

Ancient Mariner in play

I kneel only Bolton Refugee to Declare M ,what about Ancient Mariner? Return to hand , discard,or the first play decide?

thanks

The first player decides the order of passive effects. This is especially necessary when it comes to passive effects that can put cards into conflicting moribund states.

Yes, the fact that the First Player decides in this type of situation is covered in the FAQ's entry on "Simultaneous but Conflicting Entry into the Moribund State."