Four thousand years ago, it was a war between demons and devils. The devils was more powerful than the demons, and led the war in fifteen years, so the demon lord Yeenoghu understood that someone have to do something. The demon lord created a crystal that later was called "The Victory Crystal". It powered the crystal with negative energy and evil magic, and the crystal turned into seven yiamas. All yiamas has a little bit of the crystal on a necklace. If anyone remove a yiamas necklace, the yiama is destroyed. Yiamas live in The Abyss, and rarely leave its lair. It is extremely hostile to creatures that doesn’t live in its lair, and never ally with anyone. It have made its lair magical and sacred, and many adventurers dream is to look inside the lair of a yiama.

Lair Actions

The yiama lives in The Abyss, often in large, underground cavities. A yiama encountered in its lair has a challenge rating of 23 (50 000 XP).

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

• Poisonous spikes grows up from the ground. All creatures in a 60 feet cone that stands on the ground in that area must make a DC 18 Dexterity saving throw, taking 28 (8d6) piercing damage and be poisoned on a failed save, or half as much damage and no condition on a successful one. The spikes lasts until initiative count 20 next round. Any creature that moves in the area must make a DC 18 Dexterity saving throw, taking 7 (2d6) piercing damage for each 5 feet it moved and be poisoned on a failure, or half as much damage and no other effect on a successful one. A poisoned target takes 18 (4d8) poison damage at the start of its turn, and can make a DC 18 Constitution saving throw at the end of its turn, ending the effect on itself on a successful one.
• All creatures within 15 feet of the yiama must succeed on a DC 18 Intelligence saving throw or get that score reduced to 1 and be charmed by the Yiama. A charmed target rolls a d8 at the start of its turn to determine what it shall use its action to:

1. The target uses a [action]dash[action] action to move as far as possible in a random direction (roll a d8 to determine the direction)
2. The target attacks a random creature within 15 feet of it. If it isn’t any target in that area, it doesn’t do anything.
3. The target’s doesn’t do anything, but its hit point maximum gets reduced by 10 (3d6). The target dies if its hit point maximum gets reduced to 0.
4. The target dashes to a creature within 30 feet of it. If there’s no creature in that area, the target do nothing.
5. The target do nothing.
6. The target do whatever itself want.
7. The target do nothing. At the start of its next turn, this effect end for the target. In addition, the targets regains its Intelligence modifier. A greater restoration spell or other magic of 5th level or higher can make the target regain its hit point maximum.
8. The target do whatever itself wants, and the effect ends for it.  In addition, the targets regains its Intelligence modifier. A greater restoration spell or other magic of 5th level or higher can make the target regain its hit point maximum.

• The yiama chooses a creature with less than 50 hit points. That creature must succeed on a DC 18 Constitution saving throw or die. A creature killed by this effect turns into dust.
• The yiama chooses a creature within 60 feet of it. That creature must make a DC 18 Constitution saving throw, taking 88 (16d10) necrotic damage on a failed save, or half as much damage on a successful one.

Regional Effects

The region containing the legendary yiamas lair is powered with negative energy, which creates the following effects:

•  Glass, crystals, and diamonds within 1 mile of the yiamas lair crushes.
• Magma mephits are usual within 3 miles of the lair. These mephits has Intelligence and Charisma scores of 1, and are hostile to creatures that doesn’t live in the lair.
• All solid objects within 1 mile from the yiamas lair that have been there in more than one year is immune to nonmagical bludgeoning, piercing and slashing damage not made with silvered weapons. If the object been moved out of the lair, it is no longer immune to this damage.
• Wisdom [medicine] checks made to cure a disease within 1 mile of the lair has disadvantage.
• Creatures within 1 mile of the lair that eats nonmagical food or drink nonmagical water or drinks made of more than 50% water must succeed on a DC 18 Constitution saving throw or be poisoned for 1 hour. If the save fails by 5 or more, the target is unconscious for the same duration.
• When a creature takes a short rest within 3 miles of the yiamas lair, the target must succeed on a DC 18 Wisdom saving throw or only regain half of the hit points it would normally regain. If a creature takes a long rest, it must make the same saving throw. On a failure, the target regains hit points equal to its hit dice instead for regaining all hit points.
• A creature within 1 mile of the yiamas lair that isn’t born in the lair must succeed on a DC 18 Intelligence saving throw. On a failure, the creature takes 18 (4d8) necrotic damage, and the yiama gets aware for it and knows its exact position. The target is then immune to this effect for the next 24 hours.

If the yiama dies, this effects fade over the course for 2d10 days.