Swarm of Susuwatari (5e Creature)
From D&D Wiki
Swarm of Susuwatari
Large swarm of Tiny feys, neutral
Saving Throws Dex +2
Shadow Aura. The swarm causes any nonmagical light source within 20 feet of it to become less effective. If the light source normally provides bright light, it instead provides dim light while within the aura, and if it normally provides dim light, it provides no light at all. For example, a candle that normally provides bright light in a 5-foot radius and dim light for an additional 5 feet would instead produce only dim light in a 5-foot radius while within the swarm’s shadow aura.
Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny susuwatari. The swarm can't regain hit points or gain temporary hit points.
Susuwatari, or soot sprites, are tiny fey creatures that dwell in abandoned homes and gather in darkness. While harmless in and of themselves, they can be a nuisance to people exploring already dark dungeons.
Dust Motes. A susuwatari resembles a fuzzy black ball small enough to fit in a child’s palm, with two large eyes and a set of spindly little arms and legs. When startled, they scurry away at high speed, along floors and up walls. Though they are able to lift and carry objects, they struggle with anything heavier than a few pounds.
Fey Squatters. Susuwatari are drawn to dark and dusty areas, and as such they often congregate in abandoned homes and ruins. Swarms of them can coat every surface in a room, their sooty bodies absorbing most of the ambient light to make a dark locale even darker. A person who enters a room occupied by a susuwatari swarm while carrying a torch finds that the torch sheds less light than usual, and individuals with darkvision will see that every wall and piece of furniture is covered with a seething mass of blackness.
Tiny Servants. Susuwatari are sometimes summoned by other fey creatures to perform menial tasks, such as moving small items from one place to another or carrying coal to a furnace. Though they appear to find such chores fulfilling, they often struggle with their work due to their minuscule size and weakness. If another creature should stop by and assist them in their tasks, the susuwatari will be forever grateful to that creature and try to assist it in whatever small ways they can.