The Black Cauldron
The Tolkein / D&D brand of sword & sorcery common in Lloyd Alexander's classic Chronicles of Prydain was a bit dark for the Disney set, but the Mouse factory went ahead and made The Black Cauldron anyway. Too bad they Disneyfied it to death.
"...C.S. Lewis, Madeleine L'Engle, and J.R.R. Tolkein. Alexander's mythical Prydain was a land of sorcery, battle, and folklore, featuring..."