Ancient Obsidian Drake

The scales of this great beast consist of layered obsidian, dark and shining. Large, black, bone-like protrusions dot his back, shoulders, and head. He stands 20ft at the shoulders and 50ft from nose to tail. As a stone dragon, he is unable to fly; but given that his sole purpose is to guard something of great value, he doesn't seem to mind. 

Obsidian Dragons dwell in the mountains on the frayed edges of civilization. An obsidian dragon's lair is an expansive cave, cavern, or ruin that is dark and deep where it stores it's collection of nightmares taken from citizens of distant villages. Victims are dropped in a pit where the dragon's mind poison can unlock it's nightmares. The dragon feeds on fear and anguish. Nightmarish aberrations infest the dark corners of the lair, often taunting and tormenting unlucky explorers but rarely devouring them without permission from their master. Magical light and darkvision have a lessened effect within an obsidian dragon's lair. Whispers and distant screams are often heard in the shadows. 

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:

• Nightmarish shadows encircle all enemies within 60ft of the dragon. Each enemy must succeed on a DC 15 Intelligence saving throw or be under the effect of Phantasmal Force for 1 minute and immediately take 2d8 psychic damage. At the start of their turn, enemies can retry their save. While under the effect of Phantasmal Force, the enemy perceives their greatest fear as a reality and has disadvantage on all attacks except for those directed at the Phantasm. At the start of each affected enemies turn, but after they retry the save, the DM rolls from the following table to determine what effect the Phantasm has on the enemy for the round:
  
  • 1- the effect ends
  • 2- frightened
  • 3- stunned
  • 4- paralyzed
  • 5- compelled duel
  • 6- 3d8 psychic damage
• A cloud of shadow insects and bats 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 (3d6) 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 (3d6) piercing damage.
• Pools of inky, black, tar open under the feet of any enemy within 30ft of the dragon. Each tar pit is up to 10ft in diameter, centered on a point. Each enemy must succeed on a DC 15 Dexterity saving throw or be grappled. The enemy may use their action to succeed on a DC 15 Strength check to break out of the tar and move to any unoccupied space. Any enemy that moves through a tar pit before the effect ends, must roll a DC 15 Strength check and use double movement to move through it. This effect remains until the dragon dismisses it as an action, uses this lair action again, or dies. 

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 is unnaturally dark, even during the day, allowing nightmares to roam freely.
• Within 6 miles of the lair, there is a general feeling of uneasiness and enemies of the dragon are unable to benefit from short rests and regain half hitpoints from long rests.
• 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, effects fade over 1d10 days.