Swarm

It was hungry, again. The thought may only be the product of its thousands upon thousands of imaginations, but it believed it was getting hungry more often.
It knows its habitat well. It has lived there all of its col­lective lives, and knows the locations of all the best algae and the likely spots to find putrefied flesh, free for the harvesting.
But, strangely, that is not what it hungers for today. There is a tower, residing above the sewer in which it lives, a tower full of humans with strange minds and stranger devices. A tower stocked with what, to it, feels like the oddest and yet most succulent nutrients it can fathom.
It knows it must be careful, it must be hidden, as humans hate it for their unknowable reasons. It retrieves a worn robe off of a dead man, picking his bones clean as an afterthought, and dresses itself. Its constituent cockroaches rustle and smooth out the robe, roiling as a wave to raise the hood over a bodily mass that could roughly be described as its head. The man had gloves and boots, too, and so it wears them, as well, filling them with dozens of itself.
It pours through a sewer grate and slinks off into the night, working its approximation of legs in what it hopes others would see as a sickened human's walk. It keeps to the shadows, it hides the chittering mass that could be its face. Just a single bauble, it thinks. The men in the tower and their magic have so many, they would not miss one. When it feeds on such things, its thoughts always get stronger. More cohesive. More absolute.
It must always get stronger, it supposes. For who knows how strong the next thing that tries to kill it will be.

Composed of an ever-moving mass of insects or vermin in humanoid shape, a swarm is a horrifying sight for most mortals to behold. Swarms are more than the sum of their parts, forming a collective hive consciousness with an uncanny, if outright alien, intelligence, and motives and morals all their own.

One From Many

Composed of countless individual animals, the creatures within a swarm share a psychic link that allows them to operate as a single individual. Depending on what crea­tures compose them, swarms are anywhere from 4-6 feet tall and weigh 70-120 pounds. Swarms can be made up of rats, worms, locusts, wasps, cockroaches, snakes, flies, or similar, and typi­cally wear obscuring garments such as masks and over­coats to hide their form from the world. Most creatures of other races consider a swarm's amalgamated move­ment and mannerisms to be profoundly unnerving. As such, swarms typically keep to themselves, trusting only a select few.

Naturally Unnatural

Many an arcanist has theories about where swarms come from, and what conditions can imbue a collection of animals or insects with uncanny intellect and person­hood. Some believe that areas in which magic is abun­dant, such as the sewers beneath a mage's college, a dun­geon with an ancient portal to the Far Realms, or a for­gotten druid's grove, can impart small local animals with their magical potential, causing them to work together to become more than they are.
Regardless of the methods behind their animation, swarms still possess a bestial cunning, an innate under­standing that they must be ruthless to survive. A swarm rarely trusts, and is never highly social, though one can grow to accept and even support others who have shown it kindness.

Survive And Thrive

A swarm initially comes together out of pure, instinctual survival, recognizing they stand a greater chance as a collective rather than individuals. This persists once the swarm is formed, and the swarm gains the ability to survive and exist on an entirely different level. Swarms often find interests that they believe will help their survival, ranging from hunting to combat prowess to magical understanding. Utilizing its psionic talent to act as one, a swarm can communicate with others and will do so when necessary to better its chances of success.
For a swarm, it is not enough to merely survive in stagnation. A swarm becomes a swarm out of a desire to survive greater challenges, and there is always a larger threat that one can surpass.

Civilization and Culture

Naming Traditions

Aside from their own kind, swarms are not especially social creatures, and many don't see a need or use for a name. Mortals that have become swarms, however, typi­cally keep the names they held in their previous incarna­tions. Swarms that travel with others tend to acquire a name for convenience, though swarms that were never mortals usually don't truly identify with a given name. A swarm is itself, devoid of gender or other labels that would apply to more conventional beings. Names: Bespawl, Blaspheme, Blight, Chitterbox, Cringe,

Swarm

Ability Score Increase +2 Dex, +1 Int

Size Medium

Speed 30 ft.

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Age. Your constituent organisms tend to have twice their normal life spans, but as long as you replace that die off, you are effectively immortal.
Alignment. Swarms have a complex relationship with morality, often seeing no particular reason to help others. This makes them neutral, at best, with a strong tendency towards being chaotic. Mortals of other races that have transformed into swarms of their own volition are almost universally evil.
Size. Though the size of your swarm oscillates some­what, you roughly remain as large as a human.
Telepathy. You can communicate via two-way telepa­thy with any creature that is within 30 feet of you if that creature knows at least one language.
Dissonance. You can use verbal components of spells, even if you do not speak, using the chittering, writhing, or buzzing sounds of your swarm as a substi­tute. You can be affected by silence and similar as usual.
Aberrant Nature. You have two creature types: humanoid and aberration. You can be affected by a game effect if it works on either of your creature types.
Reconstitute. When you take a short rest and would expend hit dice to heal, you can call to vermin of your type in the surrounding area to reconstruct your form. If you do, roll 1d4 - 1. During this short rest, you can maxi­mize the value of a number of hit dice of your choice equal to the result of this roll.
If there is a nearby dead humanoid or beast of Small size or larger for the duration of the rest, you can also consume their body as part of this ability. If you do so, roll 1d4 + 1 instead of the initial roll for this ability that you would otherwise make. Once you use this ability, you can't use it again until you take a long rest.
Amorphous Form. As an action on your turn, you can break apart into an amorphous swarm of your constituent creatures, dropping on the ground any items you were carrying or wearing. This amorphous form has resistance to bludgeoning, piercing, and slashing damage; can fit through a gap 1 inch in diameter, and otherwise uses your statistics.
While you are in an amorphous form, you cannot attack, cast spells, or use actions other than the Dash, Disen­gage, or Dodge actions, or taking an action to reform yourself into your regular shape. You can maintain this form for up to 1 minute, after which you take 1d10 psychic damage that cannot be reduced or ignored for each minute thereafter that you remain in amorphous form, as the constituent bodies of your form slowly assert their independence and break away. If you are reduced to 0 hit points while in amorphous form, you begin making death saving throws as usual. If you stabilize or regain hit points after being reduced to 0, you automatically reassume your normal form without any additional action. Once you use this ability, you require a short or long rest before you can use it again.
At 5th level, you can use this ability as a reaction if you drop to 0 hit points while in your regular form, as­suming your amorphous form and gaining a number of hit points equal to half your total character level, rounded down. If you use this ability as a reaction, you cannot use it again until you have taken a long rest.
Amorphous Talent. While you are in your amorphous form, you gain an additional ability, depending on the type of creatures that make up your body. Choose one of the following options:
Biting. You gain a bite attack as a natural weapon. This bite can add your choice of either your Strength or Dexterity on rolls to hit, and deals piercing damage equal to 1d6 + your choice of either your Strength or Dexterity modifier. You are able to use the Attack action to use this bite.
Burrowing. You gain a burrow speed equal to your movement speed. You cannot assume your normal form while burrowing.
Buzzing. YYour movement speed becomes 10 feet, but you gain a flying speed of 25 with the hover property.
Multitudinous. You gain temporary hit points equal to your Constitution modifier + your proficiency bonus.
Skittering. You cannot be the target of opportunity attacks.

Languages. You cannot speak, but you can under­stand, read, and write Common and one other language of your choice.

Swarms That Were Mortal

Occasionally, a mortal will seek to give up the substance of what they are, and instead, become a swarm. Typically such mortals are spellcasters and do so in a bid for greater power. Depending on what they become, these swarms are often known as larva mages, rat-kings, or similar.
A mortal can also be cursed to become a swarm by another, in a ritual profane beyond description. An evil spell­caster can induce vermin to eat away at the victim's body, causing the resulting swarm to become a prison for the unfortunate individual's mind. The motives of the spellcaster in this vary wildly, but many act out of spite, revenge, or simply to create horrific manifestations of an evil entity such as Kyuss or Baalzebul without sacrificing their own mortality.
Once cursed, a mortal often has no choice but to hide from society, mourning what they have lost and what they have become. There is no easy path to regain their mortality, shy of a wish spell. Most mortals cursed in this way either live lives of seclusion or wander the shadows of the world, searching for a miracle to return them to what they once were.