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.
"...Hurt, John Huston, Nigel Hawthorne, Lindsay Rich, Grand Bardsley, Susan Sheridan. In the elite inner circle of children's fantasy..."