This is a bit of an old thread, but I ran Black Fang's Dungeon for my second time.
My players, to my surprise beat the hell out of Black Fang... I had to make up something quick to tell them when they got to the town. (I had a good story to tell them when the got home, but that was out the door with them killing the dragon)
This was all just by chance, none of this was planned or done to maximize their chances to win. One of the rogues who happened to go into the warren with Black Fang to snatch up the treasure first, triggering the acid breath. She happened to have the Energy Heart that protected her and she also made her saving throw. NO DAMAGE.
The fighter, Valeros knew about the soft belly (+2 attack), had the dragons bane (+2d6) so, if i remember right, for attack he had a +5 and a +2, for damage, I used 1d8 + 3 + 2d6. He hit 3 times for over 18 points of damage each. He survived the attack by pure luck because of low roles by Black Fang. Any damage he did receive was healed by the Cleric, Kyra who was staying a good distance from the Dragon. When the dragon was under 26 hp, I tried to have him run for his life. But the players opportunity attacks HIT! Clearing any hit points he had left.
I described the event saying that Black Fang began to flap his wings, obviously getting ready to flee using the hole in the roof of the cave. The wind made it difficult for the players to hold there ground. But as Black Fang was about to leap away, the adventurers take wild swings to do any damage in a last ditch effort before Black Fang could escape. To all of their surprise, they slash and pierce his underbelly and Black Fang makes it only a few dozen feet before he falls lifeless to the cave floor.
The rogues dissected the crap out of the dragon. And I'm trying to figure out what to do with all of those parts. I think I will make some side adventures using what she found.