When flipping through channels on TV I caught a quiz. One of the candidates was apparently a huge Disney fan visiting Disneyland (in Paris) once a month. When the quizmaster asked him if there were Disney movies he didn't like, he replied there were a few he didn't like that much. When asked for an example, I would have expected him to say the (IMO) unwatchable Song of the South, but no. He mentioned 'The Black Cauldron'. Maybe not that surprising that he picked it, seems like die hard Disney fans and the company itself do their best to keep movie as obscure as possible. Yeah ok the movie has really some pacing and continuity problems. In my opinion that is not due to bad writing but censorship. And as usual there is the obligatory sidekick (but the level of annoyance is tolerable) Despite this it still delivers a solid dark story atypical for the Disney company.
Fits in the sword and sorcery I guess, Box

The 80s brought a few other darker animations which I love to revisit when I'm getting tired of these zippy da do dah happy stuff blown in my face:

Fire & Ice: another one that fits the sword & sorcery bill well I think, no nudity but Teegra's outfit leaves little to the imagination, Darkwolf is an awesome character too

The Last Unicorn: maybe not the most developed story and characters but one of the first animations that always stuck with me since I saw it as a child on TV (in German actually), that scene with the tree was pretty disturbing though

Secret of NIMH: One of the first animations I saw on VHS, when we didn't have a VCR yet and had to rent that as well, silliness is kept to minimum. Not as dark as Watership Down but nice dark atmosphere from Don Bluth

The Great Mouse Detective: like NIMH starring mice and rats this one I actually saw in theatre before I saw the aforementioned. Based on Basil of Baker Street, it has this dark Victorian style I love. A rather gruesome scene where a cat eats a mouse (only seen in the shadow but shocking nevertheless)

The Dark Crystal: not really animation but it's hard to call this live action either. Also seen as rental first. Has some really creepy scenes with essence sucked from poor peaceful beings, an emperor that literally falls apart

Not 80s:

The Rescuers: Yeah the alligators are hilarious while they should be scary but the swamp delivers the dark atmosphere and Medusa is one of the creepiest female villains IMO

Coraline: unlike Monster House and The Corpse Bride which focuses more on weirdness and silliness, this modern digital animation delivers a dark atmosphere and story, the idea of sewing buttons on replacing one's eyes, sounds really cruel, Coraline's other mother she really is scary

Any others that should be added to the list?