The key points I remember are. Xander rescues the goddess Isis, she takes on the shape of a small snake... and the other that might be part of this same fic, but with my memory.... never can tell. Somehow Xander ends up becoming the High Priest for the Earth Goddess. Willow was expecting or training or had been promised that she was to become the High Priestess, but Xander does instead. Willow was not too happy.
fic/fics?? are Spander of course.