Abyssal black dragons have spent enough of their lives in the depths of the Abyss that it has seeped into their being. If they survive the harsh conditions, they grow protrusions on their back that, at first glance, look like gravestones. Normal black dragons are cruel, violence-loving beasts and the added Abyssal nature guarantees that these monsters delight in causing pain and misery. Like black dragons, they can dwell in swamps on the frayed edges of civilization, but they could also make their lair underground, in a place that reminds them of the Abyss.

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:

• Necrotic energy arcs, forming a 5-foot-wide line between two of the lair's solid surfaces that the dragon can see. They must be within 120 feet of the dragon and 120 feet of each other. Each creature in that line must succeed on a DC 15 Dexterity saving throw or take 10 (3d6) necrotic damage.
• Volcanic gases form a cloud in a 20-foot-radius sphere centered on a point the dragon can see within 120 feet of it. The sphere spreads around corners, and its area is lightly obscured. It lasts until initiative count 20 on the next round. Each creature that starts its turn in the cloud must succeed on a DC 13 Constitution saving throw or be poisoned until the end of its turn. While poisoned in this way, a creature is incapacitated.
• 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 ground becomes pitted and treacherous, and any plants wither and die.
• 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, the effects fade over 1d10 days.