This isn't a swarm of tiny creatures, but I did write two hive-mind races for a homebrew campaign I was working on a while back that kind of fall into this category. I was surprised by how much of Faolyn's spitballing was near spot-on for what I already did for one of them. (I ended up mostly scrapping the idea because it became more complicated than I wanted to deal with as a DM.)
Tzormic
Tzormics are essentially human-sized, anthropomorphic ants with a few fungal characteristics. You are a group of three creatures, the "Queen" body (the center of the hive mind) and two "consorts" (drones that share an intelligence equally with the Queen). Your Queen is Medium, your Consorts are Small.
All of your bodies share your Action, Bonus Action, and Reaction. This means that you may perform any Action, Bonus Action, and Reaction available to you on any given turn (or round, for reactions), but doing so prevents any of the other bodies from performing that action that round. (In addition, the body you are performing an action from must be capable of performing that action—for example, if you attempt to cast a spell with a material component with one body but it is not carrying a spell focus or the specific component, you may not cast that spell from that body.) If you take the Move action you may move all three bodies, and taking the Dash action allows all three bodies to move up to twice their base movement speed.
You roll initiative once and each body shares initiative in combat.
Each body is treated as its own physical entity, but the group is treated as one mental entity. This decision more complicated than I wanted it to, but it resulted in traits like the following:
- Effects with WIS/INT/CHA saves affect each body equally regardless of which is targeted, but STR/DEX/CON saves affect each body individually
- Each body was able to have slightly different physical stats, but not mental stats
- Each body shares awareness simultaneously (so you see, feel, hear, etc from each body at the same time), but Consorts that are ever more than a mile from your Queen are immediately incapacitated until back within range
- Each body had its own hit point pool (reduced for Consorts)
- Each body required its own equipment and consumed its own Supply
- If a Consort died then you lose the Consort (and some other traits directly connected to Consorts); if the Queen died then all bodies immediately die
- All bodies equally share proficiencies, class features, feats, etc, and you may use separate bodies to meet the requirements for rules, feats, and class features that require another creature nearby—such as flanking—but you are still limited to one Action or Bonus Action/turn and one Reaction/round
Slain Consorts may be restored at a rate of 1/long rest.
Gifts for the heritage included:
- Unstable Flight: Queen gets a flight speed, Drones get a slower flight speed. Must move at least 10 feet each turn to maintain flight or you fall at the end of your turn. No medium/heavy armor. May only fly for a limited number of consecutive turns.
- Advanced Eyes: Gain Darkvision and an expertise die on Perception checks per living Consort body.
- Warlike Carapace: Natural AC and a natural weapon.
- Dispersed Intellect: If the Queen body is ever killed but any Consorts still live, you may designate one Consort body as the new center of your hive mind. If that Consort dies before it can undergo a metamorphosis to become a true Queen you die, even if the other Consort still lives. You may undergo a metamorphosis to transform that Consort into an identical copy of the Queen body, but it takes two long rests.
- Coordinated Attacks: If two of your bodies (Queen or Consort) are within 5 feet of the same creature, you have Advantage on the first attack you make against that creature that round, provided one of the aforementioned bodies makes the attack.
Paragon Stuff:
- Improved Activity: +1 Bonus Action or Reaction/round (but not both).
- Flight: Either grant the previous Unstable Flight feature or grant an improved version of it (with Hover).
- Split Focus: Provided you have at least two bodies alive, you may designate a single body to concentrate on a spell and may concentrate on two different spells (one per body).
- Greater Hive: Gain an additional drone. Your drones become much more resilient to damage.
Jhar-Voor
This was another hive mind I worked on for the same campaign, taking a different approach—one that feels a lot less hive mind, to me, than the above. Rather than playing the center of the hive mind you play a drone. The unique nature of this hive mind is that you cannot have your drones in the same region as another drone otherwise one becomes incapacitated; in addition, the flavor of this species is that, due to paranoia, they never allow their drones to return "home" to the center of the hive mind after being sent away, due to the risk of the center of the hive mind being discovered and killed, with the intended effect being that you never have two bodies in one place at the same time. You control the other two drone bodies in an abstract way, determining with your DM where they are traveling, what they are seeing, what they are doing. They could earn money for the character you control, gather information, go on side quests for you, etc.
