Double, Double, Toil and Trouble!
A Necromancer's Grimoire: Secrets of the Witch provides a wide variety of new content for anyone who likes witches, including new hexes, alternate familiar special abilities, and a number of new and interesting feats. Further, it provides a new 20-level base class for characters interested in playing as a green hag, which grants them all the powers of a normal green hag over the first eleven levels, and then grants new green-hag-themed abilities for the remainder of the class.
The book isn't just for witches, however, and its main focus is something any arcane spellcaster can appreciate: a wide array of feats and spells designed to allow spellcasters to form covens-groups of spellcasters who work together to collaboratively cast spells. Though casting as a coven requires some effort, it allows casters to master far more powerful spells than they would be able to on their own.
From the makers of Advanced Arcana Volume I and The Ebon Vault: Orbs of Power, A Necromancer's Grimoire: Secrets of the Witch provides you with rules for playing a green hag character, everything you could want to customize and flesh out your witch, rules for casting spells as a coven, and 30 new spells designed to be cast collaboratively, and makes a fine addition to any mage's library.