Black dragon

Black dragons are less vain than other chromatic dragons, but they are especially sadistic: they enjoy torturing creatures they see as beneath them.

Appearance
Aside from their black scales, which turn from glossy to dull as they age, black dragons are distinguished by their skull-like faces, with deep eye sockets and broad nasal openings; the face gets more skeletal with age, as the flesh around its horns and cheekbones recedes. Even their blood is deep purplish-black and their stomach is extremely acidic, known to dissolve some of the hardiest of creatures.

The outward appearance of Umbrasyl, an ancient black dragon, was not described in much specific detail during his appearances, aside from having a thick hide and a horned face.

Abilities

 * Acid Breath: A more toxic and concentrated acid that does not comes from a black dragon's stomach, producing in a separate gland.
 * Bite
 * Claw
 * Tail Attack
 * Wing Attack

Lairs
Black dragon lairs have pools of murky, greenish-brackish acid. Seemingly from these pools can emerge clouds of biting, stinging insects, and the pools themselves can animate and reach out for nearby enemies. Black dragons can also conjure magical darkness in their lairs.

Known black dragons

 * Umbrasyl the Hope-Devourer: An ancient black dragon and a member of the Chroma Conclave, slain by Vox Machina and Shale.
 * Guuthal the Ever-Fed: Previously an ancient black dragon, then a dracolich, active during the Age of Arcanum.
 * Oracs: Previously an ancient black dragon, then a dracolich who lives in the ruins of Ghor Veles, from where he extends his power into the Miskath Strand.
 * Thardraxxus: An inhabitant of the Rootgarden Marsh (east of Mooren Lake), allied with the sentient manawort mushrooms there.

Campaign 1: Vox Machina
Umbrasyl joined the Chroma Conclave and participated in the initial attacks on Emon (destroying the only evidence recovered from the Ruins of Vos'sykriss, just brought back from Visa Isle) and presumably Draconia. He then took over Westruun, making short work of the Shields of the Plain, made his lair on Gatshadow Mountain, and when the Herd of Storms under Kevdak opportunistically moved into the fallen city, Umbrasyl tasked the Herd with extracting treasure from the city.

Vox Machina deposed Kevdak, installed Zanror as the new leader, and persuaded what remained of the Herd to help kill Umbrasyl. Umbrasyl escaped an initial ambush by Vox Machina, the Herd of Storms, and Noja, but was subsequently slain in his lair by Vox Machina and Shale, with Grog Strongjaw landing the killing blow.

Tal'Dorei Campaign Setting and Tal'Dorei Campaign Setting Reborn
Following his death, Umbrasyl's acidic blood, magical in nature, seeped into the corpses of a dozen goliath scouts from the Herd of Storms. Combining with the "foul power" of Gatshadow, it transformed the goliaths into undead, black dragonblood revenants. The dragonblood, called the Black Snow tribe, instinctively flew to the Ashen Gorge using their skeletal wings, drawn to the Ruby of Oblivion, a ruby of "immense unholy power". In 836 PD, it was stored in the Obsidian Geode of Ashen Gorge, a treasure vault guarded by golems and elementals.

The Mighty Nein found several undead followers of Oracs who had been displaced to Rumblecusp, but destroyed them without learning anything useful.

Trivia
One of the Vestiges of Divergence, the Armor of the Valiant Soul, is largely crafted from black dragon scales.