I continue to maintain that the Castle is a sort of Queen, tapping the flame of the Dyne. So the concept of "tap source of earth magic, get really powerful" has been with us since early on.

Just in case it wasn't a joke, The Other is one of Lucrezia's titles. The avatar was of The Other, not the other queen. Now since she has several bodies, it is quite legitimate to refer to the other The Other.

What will Agatha's relationship with Albia be like once they return to England? We're going to find out if she's a good witch or a bad witch.