Truly a frightening thought. Those familiar with the Planescape setting will receive scant information on Night Hags, but the book covers them briefly. Another type of powerful hag, the undead Spectral hag is also brought forth to light with more detail and information that has been available previously. The second section though, is perhaps of more universal worth for it covers witches and warlocks. Unlike previous attempts at defining these characters, this book almost makes them a second class that the character has.
Males are warlocks and can cast spells from a limited number of wizard schools.
Females are witches and can cast clerical magics from a few spheres. There are other limitations which make sure that while the class is indeed powerful that it is well balanced. These witches are a secretive lot which allows the GM to put them into the campaign without a lot of continuity issues. Too many times I've pondered over how such a powerful kit or ability could be unknown till know. There background fits in well with any world and can be used to add a little spice to the game.