The Willow Sourcebook (1988)

From the cover:

In a land of sorcery, a baby is born. Legend foretells the child, Elora Danan, will destroy the evil ruler, Queen Bavmorda. But Bavmorda is determined to destroy Elora first. All Bavmorda's armies, led by General Kael and Princess Sorsha, go forth to find the child.
Willow Ufgood, a gentle Nelwyn farmer, becomes the baby's reluctant guardian. Together with brave companions -- he renegade swordsman, Madmartigan; the brownies, Franjean and Rool; and the sorceress Fin Raziel -- Willow embarks on a quest to keep Elora Danan from Bavmorda's clutches...
Explore a world of magic, of heroes and villains, of cruelty and courage. Explore the world of Willow.

The Willow Sourceebook Includes:
Detailed histories of Willow, Madmartigan, Bavmorda, and every important character from the movie.
The cultures and beliefs of the Nelwyns, the soldiers of Nockmaar, the Knights of Galladoorn, the fairies, and the brownies.
Fearsome monsters -- the two-headed Eborsisk, the Death Dogs, and others.
Magic-transformation, Bavmorda's Ritual of Obliteration, Cherlindrea's Wand, and more!
Descriptions of the lands, people, and cultures of the world of Willow, including Tir Asleen, Bavmorda's Nockmaar, and Nelwyn Valley.
A detailed map of the lands travelled in the movie.
Game information that lets you use the people and creatures of Willow in your own fantasy roleplaying game.

Plus 8 pages of full-color photographs from the movie!