The Bloodstorm
CREATURE 14A hundred thousand leeches, mosquitos, and parasites form a roiling mass of hunger and malice. It moves like a storm through the tunnels and caverns of the Emperor's Peak, constantly in search of its next meal. Though it has many bodies, it has just one, startlingly clever mind. The flames and smoke of the cities keeps it at bay, but in the darkness, it is at home. The dwarves of Highhelm have learned how to live with the threat, but those traveling deeper into the mountain must always remain vigilant.
In the swamps of the Tanglebriar, food is difficult to come by. So when a grievously wounded demon, a shemhazian known as Gratheyr, fled into its waters to escape from his enemies, every starving creature swarmed at the smell of blood. As the creatures devoured his flesh, they were corrupted by his Abyssal blood, and their hunger only grew. They feasted until nothing but his heart remained, still beating at the center of the swarm, binding it to a single will. With its meal finished, the bloated swarm left the swamp in search of its next prey. It moved aimlessly, hunting animals and travelers alike, until a great rumble beneath the earth attracted its attention. The Bloodstorm followed the vibrations deep underground, toward the scent of sweat and the sounds of voices.
Tremorsense allows a monster to feel the vibrations through a solid surface caused by movement. It is an imprecise sense with a limited range (listed in the ability). Tremorsense functions only if the monster is on the same surface as the subject, and only if the subject is moving along (or burrowing through) the surface.
The Bloodstorm can precisely sense bleeding creatures within 120 feet.
The monster deals the listed amount of damage to any number of creatures Grabbed or Restrained by it. Each of those creatures can attempt a basic Fortitude save with the listed DC.
Each creature in the Bloodstorm's space takes 3d6 piercing plus 3d6 slashing damage (DC 31 basic Fortitude save). Creatures that fail their saving throw also take 1d8 persistent bleed damage.
The swarm condenses into the solid shape of a shemhazian demon. While in this form, it's a gargantuan creature, cannot share the space of another creature, and can use its pincer attack. It loses its resistance to physical damage as well as its weaknesses to area and splash damage. Any creatures sharing a space with the Bloodstorm when it transforms are pushed into the nearest empty space. The Bloodstorm can use this action again to revert to its swarm shape.
The monster can instead use Improved Grab as an action and choose one creature it's grabbing or restraining with an appendage that has Improved Grab to automatically extend that condition to the end of the monster's next turn.