From publisher blurb:
The Book of Familiars -- Familiars for All Classes. All those who tread the paths of the wild, who crawl through the lost dark, plunder treasures of the ancients, must surely find themselves alone and bereft of friends. It is in those moments, when the cold creeps up your spine, and the hair rises, that you most need a stalwart companion at your side; a wolf to bare fangs, an owl to see into the darkness, a muse to whispers songs of the ancients, a named sword of cold steel and magic . . . these are the familiars you seek.
An Arm Extended -- The Book of Familiars offers a groundbreaking look at Castles & Crusades' thirteen core classes. Herein we expand the horizons of familiars and have developed a fully functional, well balanced approach for each character class to gain a familiar or animal companion. These added features do not inhibit the simplicity of the Siege Engine, nor do they add a level of complexity to your game that slows it down. The Book of Familiars adds new dimensions to the game without impeding play.
And these are not the familiars you know. However, the Book of Familiars breaks the fantasy mold. From the barbarian's spirit guides, to a fighter's weapons, the monk summoning ancestral spirits, or a rogue's shadow with a life its own and the paladin fusing his own spiritual power with his arms and armor. These are familiars as you've never seen them.
Complete with over 150 animals and monsters.