Homebrew Hive of Cranium Rats in a Mech Species Details
When normal rats are bombarded with psionic energy, either intentionally or unintentionally, cranium rats are the result. Cranium rats are somewhat smarter than ordinary rats and behave as such. If enough cranium rats come together to form a swarm of cranium rats, they merge their minds into a single intelligence with the accumulated memories of all the swarm’s constituents. The rats become smarter as a result, and retain their heightened intelligence for as long as the swarm persists. The swarm also awakens latent psionic abilities within each cranium rat, bestowing psionic powers upon the swarm .
Some mind flayer colonies create cranium rats to use as spies - the rats invade communities and act as eyes and ears for the colony’s elder brain, transmitting their thoughts when the swarm is within range of the elder brain’s telepathy. Other times, a swarm of rats may nest below a gem dragon's lair or some other creature with a massive psionic presence, unintentionally creating a cranium rat hive. Outside the control of these more powerful beings, swarms of cranium rats can develop their own personalities and even form communities with other swarms of cranium rats that have grown to a significant enough size. These communities are rare, but those that have formed can vary wildly in size, structure and ideology.
When a single swarm decides to leave its home and venture out into the greater world, their unusual appearance and alien origins can make it difficult for them to interact with other sentient creatures. Thus, a practice has spread between cranium rat hives of building humanoid-shaped machine bodies, called mechs, for the swarm to travel in and to better interact with a world built for larger, single-bodied creatures. It remains a mystery as to how this practice has spread between the rare and varied cranium rat communities, scattered as they are over vast distances and even on other planes. It is disconcerting to think about what other ideas may be spread this way, and how separate these communities and swarms actually are.
A hive of cranium rats in a mech communicate telepathically, “speaking” as one creature, often referring to itself using the collective pronouns “we” and “us.”
Creating Your Character
At 1st level, you choose whether your character is a member of the human race or of a fantastical race. If you select a fantastical race, follow these additional rules during character creation.
Ability Score Increases
When determining your character’s ability scores, increase one score by 2 and increase a different score by 1, or increase three different scores by 1. Follow this rule regardless of the method you use to determine the scores, such as rolling or point buy. The “Quick Build” section for your character’s class offers suggestions on which scores to increase. You can follow those suggestions or ignore them, but you can’t raise any of your scores above 20.
Languages
Your character can speak, read, and write Common and one other language that you and your DM agree is appropriate for the character. The Player’s Handbook offers a list of languages to choose from. The DM is free to modify that list for a campaign.
Creature Type
Every creature in D&D, including each player character, has a special tag in the rules that identifies the type of creature they are. Most player characters are of the Humanoid type. A race tells you what your character’s creature type is.
Here’s a list of the game’s creature types in alphabetical order: Aberration, Beast, Celestial, Construct, Dragon, Elemental, Fey, Fiend, Giant, Humanoid, Monstrosity, Ooze, Plant, Undead. These types don’t have rules themselves, but some rules in the game affect creatures of certain types in different ways. For example, the cure wounds spell doesn’t work on a Construct or an Undead.
Life Span
The typical life span of a player character in the D&D multiverse is about a century, assuming the character doesn’t meet a violent end on an adventure. Members of some races, such as dwarves and elves, can live for centuries. If typical members of a race can live longer than a century, that fact is mentioned in the race’s description.
Height and Weight
Player characters, regardless of race, typically fall into the same ranges of height and weight that humans have in our world. If you’d like to determine your character’s height or weight randomly, consult the Random Height and Weight table in the Player’s Handbook, and choose the row in the table that best represents the build you imagine for your character.
Hive of Cranium Rats in a Mech Traits
As a hive of cranium rats in a mech you have the following racial traits.Creature Type
You are swarm of Tiny aberrations (Cranium Rats). While in your mech, you are considered a humanoid and affected by all abilities that affect this creature type in addition to aberrations.
Size
You are Medium while in your mech.
Speed
Your walking speed is 30 feet.
Mech Suit
You are a hive of cranium rats who have constructed and collectively pilot a mech suit. The mech suit is Medium size and should be considered the bearer of all physical statistics on your character sheet (strength, dexterity, constitution and hit points), and whenever out of the Mech Suit, the swarm is considered in Swarm Form (see below). If your mech is destroyed, you require one month to rebuild it and must have access to blacksmith tools and a full set of new armor (if intending to use armor), which is consumed in the construction. The mech suit can be equipped with any armor set you have proficiency with using blacksmith tools, but the armor is consumed in the construction. If unarmored, the mech suit is made of cloth and wood struts or something similar. You require one day of work and blacksmith tools to install a new set of armor onto your mech, replacing the previous armor.
Hive Psionics
You know the mage hand cantrip, and the hand is invisible when you cast the cantrip with this trait.
Starting at 3rd level, you can cast the command spell with this trait. Starting at 5th level, you can also cast the detect thoughts spell with it. Once you cast command or detect thoughts with this trait, you can’t cast that spell with it again until you finish a long rest. You can also cast either of those spells using any spell slots you have of the appropriate level.
Intelligence, Wisdom, or Charisma is your spellcasting ability for these spells when you cast them with this trait (choose when you select this race). None of these spells require spell components when you cast them with this trait.
Psychic Resilience
You have resistance to psychic damage.
Reduced Darkvision
You can see in dim light within 30 feet of you as if it were bright light, and in Darkness as if it were dim light. You can't discern color in Darkness, only Shades of Gray.
Mech Builders
You have proficiency with Smith's Tools.
Telepathy
You cannot physically speak any languages, but you are able to speak telepathically to any creature you can see within 60 feet of you. Your telepathic utterances are in a language you know, and the creature understands you only if it knows that language. Your communication does not give the targeted creature the ability to respond to you telepathically.
Swarm Form
You may, as an action, choose to leave your mech (it continues to stand in place) and act as a swarm. You retain the features above and your mental characteristics. You take on all the physical statistics and features of a Cranium Rat Hive (swarm form) below, similar to a druid’s wild shape ability, with the exception that if you are reduced to 0 hit points, you fall unconscious and must begin making death saving throws as normal.
Cranium Rat Hive (swarm form)
Medium swarm of Tiny Aberrations (Cranium Rats)
Armor Class 12 (natural armor)
Hit Points 2 times your player level
Speed 30 ft., burrow 10 ft.
Damage Resistances bludgeoning, piercing, slashing
Condition Immunities grappled, paralyzed, petrified, prone, restrained
Senses darkvision 30 ft., passive Perception 10
Languages telepathy 60 ft.
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 rat. The swarm can't regain hit points or gain temporary hit points.
Small Hands. As a swarm, you are unable to use normal weapons and armor. You may only use normal-sized equipment or magical items at your GM's discretion. You cannot hold or use more than a single intelligent rat would be capable of.
Actions
Bites. Melee Weapon Attack: +PB to hit, reach 0 ft., one target in the swarm's space. Hit: 2d6 piercing damage, or 1d6 piercing damage if the swarm has half of its hit points or fewer.
Spellcasting. As long as it has more than half of its hit points remaining, you may cast spells you know. However, as a swarm you cannot cast spells requireing material components.
Bonus Actions
Illumination. The swarm sheds dim light from its brains in a 5-foot radius, increases the illumination to bright light in a 5- to 20-foot radius (and dim light for an additional number of feet equal to the chosen radius), or extinguishes the light.
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