Mercedes Trailer

The curse was mobile, it followed Mercedes back to Eyurel. Rien was originally part of the main continent but broke off with the ice after it was frozen over. The fact that Aran was there might mean that the fight happened between the time Aran got injured and was sent back, and when they sealed the Black Mage.

I guess I can go with it parting off. I am guessing they pulled the black mage outside at some point though because even though the curse is mobile (as we see with Mercedes's plot line) It doesn't seem to have nearly a strong effect on her town as it did to Rien which I don't think was inside of the temple.