Yarghuul Broodmother

Yarghuul Broodmother
As soon as a yarghuul broodmother breaks from its shell it takes ownership of the brood and begins to expand its nefarious influence. The once limited number of yarghuul quickly starts to rise, as the broodmother births aberrations from its corrupted tumours. The brood becomes more aggressive as it expands to assimilate new territories, always gathering more organic materials to feed the broodmother. A broodmother is a huge heap of milky white flesh, it is limbless and mounted by a head with no eyes and a mass of tentacles. It is barely mobile and relies on its brood to protect it. It sings almost constantly an entrancing eerie sound out of the many holes of its skin, luring those that hear it.
Fallen Sky. In the tales of old is a peculiar legend that speaks of a night when the sky was alight, basked in strange greens and greys colours. Then, tears from the heavens showered the world, comets, and meteors of various sizes. Strangely few of them were found, most dissolved in a matter of hours or sunk deep beneath the earth, leaving barely any trace of their existence. However, soon after the land became sick, grey, colourless and mutated. Beings emerged out of nodules of the remaining meteors, pouring out like white slime before taking the shape of squat, pale, toadlike creatures, superhumanly strong and noxious-smelling, having no eyes but instead a mass of tentacles at the end of their snout.
Toxic Brood. Yarghuul are aberrations that transform their surroundings into toxic wasteland, choked with patches of creeping and gibbering mounds of organic matter. They thrive in the desolation they create and bask in its strange glow. As such, they are rarely found in healthy lands and their presence means that a region is contaminated. They are very territorial predators, attacking on sight any living thing. They are often found in broods of five to ten creatures, but much larger broods have been discovered as well, truly infesting nightmarish regions of the deep Underdark. Their social hierarchy is nebulous at best, as they almost never communicate with other creatures, but they seem to share a hive-mind mentality.
Mother of the Brood. A Yarghuul infestation usually follows a simple scenario: they gather in a small brood and soil the area over time by their mere presence. Once their surrounding has mutated to their liking, they establish a nest. The brood scavenges any kind of materials and organic life they can and shape a large “shell” from their findings. Once the shell is completed and sealed, half of the brood will liquefy and infiltrate it, merging inside the shell. At that moment, the brood is the most vulnerable, its numbers depleted. Soon after, the shell will start emitting blinding light and deadly energy, vaporizing any that come too close. About a week later, a single yarghuul brood mother emerges from the shell, ready to lead the brood.
Telepathic Defiler. Yarghuul are driven mainly by instincts and are savage and direct in a  fight: they rush, devour and secrete toxic slime through the large pores of their skin. However, they are no mere beasts and work with other members of the brood to corner prey and identify the greatest threat. If mounting an ambush, they will use their mutable form to devastating effect, falling from the ceiling or emerging from the ground to surprise their victim. Members of a yarghuul brood use a complex combination of telepathic images, whale-like singing and bioluminescent pulses from their tentacles to communicate with each other.

Broodmother's Lair
A brood of yarghuuls often make its lair near the landing site of the meteor they emerged from. Therefore the lair is usually located in a crater, chasm, or cavern. It is a toxic wasteland, covered with creeping colourless organic matter and alveolar structures of unknown purpose.
Regional Effect
The corruption and ravage of the brood transforms the region surrounding the brood’s lair, creating the following effects:

• Plants and animals raised within 6 miles of the brood’s lair have twisted, tumorous aberrant deformities.
• Mounds of various sizes of twitching organic matter can be found within 2 miles of the brood’s lair. Gibbering mouthers often lurk near them.
• The region within 2 miles of the brood’s lair basks in dim light, this eerie white luminescence has no apparent origin. Any creature that isn’t an aberration feels nauseous and uneasy while in the region.

If the brood is destroyed, these effects fade over 1d10 years.
Lair Actions
On initiative count 20 (losing initiative ties), the broodmother can take a lair action to cause one of the following effects; it can't use the same effect two rounds in a row:

• The broodmother vanishes, fusing with the organic matter that covers its lair. The broodmother can end this effect at the start of any of its turns, reverting to its true form once more and appearing in any location it chooses within its lair. While transformed, the broodmother is incapacitated, and it can't be targeted by attacks, spells, or other effects. The broodmother can't use this ability outside its lair. All creatures it had swallowed are freed, falling prone in a space within 10 feet of the space the broodmother left.
• A gibbering mouther appears on a spot on an unoccupied space on the ground that the broodmother chooses within the lair. The gibbering mouther is destroyed on initiative count 20 on the next round.
• A 20-foot-square area of ground within 120 feet of the broodmother sprouts tentacles until initiative count 20 on the next round. Any creature that starts or ends its turn in the area must succeed on a DC 18 Strength saving throw or be restrained. A creature can escape the tentacles with a successful DC 18 Strength (Athletics) or Dexterity (Acrobatics) check as an action.