Manifesting as a gigantic snake with the arms of a man, or sometimes a reptilian humanoid creature, Yig is considered to be the god of snakes and serpents everywhere. He feels a fierce devotion to his "children," emerging from his sleep every autumn to punish those who harm them. He does this either by turning them into serpents or serpent-like wretches themselves, or simply sending other snakes to kill them when they sleep.

The arid serpent hills are home to the Father of Serpents, Yig. A perpetual fog hangs in the air over this decrepit landscape. Dense thickets of vines, covered in needle-sharp thorns, stretch from hill to hill. Crocodiles, easily mistaken for one of many fallen trees which direct the light flow of dark murky water, pose significant threat to what little game inhabits the treck into the heart of these hills.

At it's center, the serpent hills open into a vast, damp, dark cave system, hidden from prying eyes by dense thorny vines and fallen trees. Here he sleeps, waiting for the cool, yet bearable months of autumn to exact his vengeance on those who would harm his brood.

Lair Actions

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

• 1d4 + 1 Flying Snakes and Poisonous Snakes erupt in a 20-foot radius centered on a point on the ground that Yig can see within 120 feet of it, and enter combat. The snakes flee when Yig uses this lair action again or when it dies.
• A wall of tangled brush bristling with thorns springs into existence on a solid surface within 120 feet of Yig. The wall is up to 60 feet long, 10 feet high, and 5 feet thick, and it blocks line of sight. When the wall appears, each creature in its area must make a DC 15 Dexterity saving throw. A creature that fails the save takes 9 (2d8) piercing damage and is pushed 5 feet out of the wall’s space, appearing on whichever side of the wall it wants. A creature can move through the wall, albeit slowly and painfully. For every 1 foot a creature travels through the wall, it must spend 4 feet of movement. Furthermore, a creature in the wall’s space must make a DC 15 Dexterity saving throw once each round it’s in contact with the wall, taking 9 (2d8) piercing damage on a failed save, or half as much damage on a successful one. Each 10-foot section of wall has AC 5, 10 hit points, vulnerability to fire damage, resistance to bludgeoning and piercing damage, and immunity to psychic damage. The wall sinks back into the ground when Yig uses this lair action again or when it dies.
• Magical fog billows around one creature Yig can see within 120 feet of it. The creature must succeed on a DC 12 Wisdom saving throw or be charmed by Yig until initiative count 20 on the next round.

Regional Effects

The region containing an Elder One's lair is warped by the monstrosity’s magic, which creates one or more of the following effects:

• Thickets form labyrinthine passages within 1 mile of the Yig’s lair. The thickets act as 10-foot-high, 10-foot-thick walls that block line of sight. Creatures can move through the thickets, with every 1 foot a creature moves costing it 4 feet of movement. A creature in the thickets must make a DC 15 Dexterity saving throw once each round it’s in contact with the thickets or take 4 (1d6) piercing damage from thorns.
  Each 10-foot-cube of thickets has AC 5, 20 hit points, resistance to bludgeoning and piercing damage, vulnerability to fire damage, and immunity to psychic and thunder damage.
• Within 1 mile of its lair, Yig leaves no physical evidence of its passage unless it wishes to. Tracking it there is impossible except by magical means. In addition, it ignores movement impediments and damage from plants in this area that are neither magical nor creatures, including the thickets described above. The plants remove themselves from Yig’s path.
• Serpents and reptiles within 1 mile of Yig’s lair serve as Yig's eyes and ears. Deer and other large game are strangely absent, hinting at the presence of an unnaturally hungry predator.

If Yig dies, the serpents and reptiles lose their supernatural link to it. The thickets remain, but within 1d10 days, they become mundane plants and normal difficult terrain, losing their thorns.