Nightscale

Black dragon. Lives in the Stone Tooth. Competitive swimmer. Stuck the Aegis in her forehead for added protection and has summarily avoided being killed for a long time. Eaten many things. Probably wants to eat you too. Deterred by wealth. According to duergar, at the bottom of a hole.

Escaped with her life after an encounter with the Sovereign Dungeoneering Company. Still at large.

Description
Black dragon of uncertain gender. Once had the Aegis embedded in their forehead to keep themselves safer using its protective properties, currently no longer possesses it.

Background
Nightscale was a black dragon obsessed with avoiding death. Perhaps feeling weaker or maybe just needing some reassurance in their own survivability in a world unkind to dragons, they sought out (citation needed) or stumbled upon a magical shield known as the Aegis and carried it with them on their head. This went on for so long that shield melded with dragon and their scales grew over it. Hidden away in the Stone Tooth, a ways away from Paripas and most other northern civilization, Nightscale made their home in a lagoon at the bottom of a massive pit. Their remote location did not stop challengers from attempting to take the Aegis, however; Zuul and a bunch of his cohorts had set up camp around a gem field known as the Glittering, a sort of staging area before the descent, to make a play for the shield.

Nightscale had been known to occasionally fly out when hungry and snack on their would-be challengers. Offerings of money and wealth seemed to be a good deterrent to avoid being eaten. The way down to Nightscale's lair was not known by any of the challengers, as Nightscale would use the rivers running through the Stone Tooth to travel from floor to floor. They were a varsity swimmer.

"Superstars Sucked into the Super Massive" (1x21)
The party first learned of Nightscale from Letitia, who said that the Aegis was likely in Nightscale's hoard, guarded by them. (Interestingly, Letitia also said that the party was likely to run into duergar, orcs, and drow along the trip.) Letitia made a deal with the party: get the Aegis for her and she'd unlock Milto's vault. The party left Paripas at sunset for the Stone Tooth, teleported there by Letitia.

"We've Got a Big, Big Mess on Our Hands Tonight" (1x24)
Encountering Zuul, the party learned that Nightscale had flown up and harried his men a few times before and that they'd dealt with the dragon by throwing bags of gold Nightscale's way. After some interesting antics with a river, a fish, and a monk, the party stumbled on a settlement of duergar and was (somewhat) able to communicate with them through illusions, learning that Nightscale's lair was below-- down a massive hole-- and that they had taken many duergar lives and belongings. The duergar did not seem keen on having the party stick around and ushered them toward the lair hole.

"I Always Put Myself in Destructive Situations" (1x25)
Peer-pressured down the dragon hole by the duergar, the party descended the ladder and came upon a lagoon. Things deteriorated quickly: Awk attempted to connect with Nightscale on meaningful, personal level, Nightscale was supremely cheesed off about incursions onto their territory, battle was joined after a breath of acid raked over the party, and Harry fought acid with acid, threatening to melt the dragon's hoard with his own breath at one point. It was a very messy fight, involving a plague of insects, sneezing and choking powder, illusion work by Zeno, and the constant chance of spells ricocheting off the Aegis when cast on Nightscale and firing back at the party. During the battle, Nightscale's acid breath also hit Kheryph. Ultimately Harry cracked one of the horns off the dragon's head, then ripped off the Aegis. A wounded Nightscale fled through the west passageway, a way out only possible, they said, for dragons.

Stone Tooth dwellers
snacks, probably

Harry
would imagine not a fan