There are some minor characters in The Balck Cauldron, and to not give them credit would be wrong. For it these minor characters didn't appear in the film, then the movie wouldn't end, or be the same film as it is now.
The Gwythaints are the dragons that are in the service of the Horned king. Their job is to spy for the Horned King and take things he wants ( in other words, pignap Hen Wen ). They look like a mixture of a vulture and a pterodactyl.
The Henchmen are indeed the stupidest characters in the film. In fact, I am willing to bet that they haven't two brain cells to rub together. They would be totally lost except for the excellent leadership of Creeper. The Henchman's job in the film is to be ruthless and unmerciful, and they preform it well. In earlier trailers of The Black Cauldron, there was a Henhman named Moose, but he never made it to the screen.
Burny is the assumed name for the Guard dog who harasses Fflewddur Fflam. He provided some comic relief in the film.
The Sexy Dancing Girl appears for only a couple seconds in the Henchman dining sequence. Her job is simple: entertain the troops.
The Fairfolk appear when Taran and the gang are pulled into the whirlpool and taken into the Fairfolks' realm. They are primarly there to prove that there are indeed inhabitants there and to provide the transportation of Taran and the gang back to the surface of the realm.
