Calathanorgoth, "the old one"

The Old One (Black Dracolich): This dragon was of wyrm age when she became a dracolich; she resides in the ruins of Orogoth with her grandchildren and great-grandchildren: the venerable mated pair Wastirek and Vilholin, their son the adult Woklef and the young Aswidorg, and the mature adult females Cheleen and Kasidikal.

House Orogoth was an organization of black dragons, half–black dragon's  and related creatures headquartered at Orogoth on the High Moor. The House was originally a powerful arcanist family of Netheril, known for their interest in acquiring draconic powers, and for accidentally creating the ophidian race. Although thought lost to history, House Orogoth returned in 90 DR under the leadership of the great wyrm Calathanorgoth. Under her direction, the House sought to accumulate the secrets of Netherese magic and research ways of attaining immortality.

The House rarely accepted new members, usually only doing so if necessary for an important project. Applicants were required to have some arcane ability, though sorcerers were not tolerated. Humans who could demonstrate Netherese descent were preferred, with humans of other ethnicities tolerated but often treated with disdain. In return for faithful and proficient service to the House, members were given access to its huge library of magical lore

At Orogoth, the House maintained one of Faerûn's largest libraries of magical lore.

Magical research was a priority for House Orogoth, particularly on the subjects of Netherese magic and immortality. Several of its members sought to improve the process of creating dracoliches.

House Orogoth had a vested interest in maintaining their control over the area surrounding Orogoth. To this end, they spent considerable time and resources controlling neighboring tribes of ophidians and savage humans. During periods of intense magical research, the House turned inward, lessening the degree of control somewhat.

Orogoth was well-known along the Sword Coast—especially in Amn—as a lucrative adventuring spot, with tales circulating about heaps of gems for the taking. As such, the House was frequently targeted for plunder by the Cult of the Dragon, yuan-ti from nearby Najara, and by adventurers in general. These efforts were summarily quashed, with offenders routinely killed or transformed into beast shape.

Black dragons dwell in swamps on the frayed edges of civilization. A black dragon’s lair is a dismal cave, grotto, or ruin that is at least partially flooded, providing pools where the dragon rests, and where its victims can ferment. The lair is littered with the acid-pitted bones of previous victims and the fly-ridden carcasses of fresh kills, watched over by crumbling statues. Centipedes, scorpions, and snakes infest the lair, which is filled with the stench of death and decay.

Lair Actions

On initiative count 20 (losing initiative ties), the dragon takes a lair action to cause one of the following effects; the dragon can’t use the same effect two rounds in a row:

• Pools of water that the dragon can see within 120 feet of it surge outward in a grasping tide. Any creature on the ground within 20 feet of such a pool must succeed on a DC 15 Strength saving throw or be pulled up to 20 feet into the water and knocked prone.
• A cloud of swarming insects fills a 20-foot-radius sphere centered on a point the dragon chooses within 120 feet of it. The cloud spreads around corners and remains until the dragon dismisses it as an action, uses this lair action again, or dies. The cloud is lightly obscured. Any creature in the cloud when it appears must make on a DC 15 Constitution saving throw, taking 10 (3d10) piercing damage on a failed save, or half as much damage on a successful one. A creature that ends its turn in the cloud takes 10 (3d10) piercing damage.
• Magical darkness spreads from a point the dragon chooses within 60 feet of it, filling a 15-foot-radius sphere until the dragon dismisses it as an action, uses this lair action again, or dies. The darkness spreads around corners. A creature with darkvision can’t see through this darkness, and nonmagical light can’t illuminate it. If any of the effect’s area overlaps with an area of light created by a spell of 2nd level or lower, the spell that created the light is dispelled.

Regional Effects

The region containing a legendary black dragon’s lair is warped by the dragon’s magic, which creates one or more of the following effects:

• The land within 6 miles of the lair takes twice as long as normal to traverse, since the plants grow thick and twisted, and the swamps are thick with reeking mud.
• Water sources within 1 mile of the lair are supernaturally fouled. Enemies of the dragon that drink such water regurgitate it within minutes.
  Fog lightly obscures the land within 6 miles of the lair.

If the dragon dies, vegetation remains as it has grown, but other effects fade over 1d10 days.