Crystalmist

A single crystalmist looks like a snowflake drifting on the air, soaking up sunlight to power its crystal body. At its center a tiny point of light pulses and slowly shifts color over the course of the day. Alone, each is mindless, AC 10, with 1 hit point, no real attack and movement 18. They may signal one another crudely by changing color.

What most people mean by a crystalmist, though, is the shape a swarm takes when threatened: fifty motes pull together into a sphere about a foot across that throbs with a deep, menacing hum and glows with shimmering white light. The listed statistics describe this combined form.

Merging takes one round, during which the swarm cannot defend itself. Once formed, the globe fires a beam of stored light each round, using a normal attack roll, reaching 20 feet; past that distance the light spreads too thin to hurt. A hit deals 1d6 points of damage, doubled to 2d6 when the fight takes place under bright illumination, for example a continual light spell.

A miss that still rolls above 3 means the beam struck something the target carries, such as armor or a shield, chosen at random by the DM with an eye to size and position. A flammable object hit, like a wooden shield or padded armor, must save vs. magical fire or catch light. Burning clothes deal 1d4 points of damage per round until put out or removed, and items full of fuel, such as lanterns, have a 10% chance to explode for whatever damage the DM judges fitting.

Sleep, charm, illusion and other mind-affecting spells have no effect on it. Each point of damage kills one member, and once the globe takes 10 points it breaks apart; after 12 points, for instance, 38 survivors scatter. They cannot regroup for five rounds.

Dimmer than a grasshopper, crystalmists have no real society, yet instinct keeps them together in drifting colonies of several hundred. They reproduce rarely, splitting in two like single-celled life.

Crystalmists neither hunt nor are hunted, though a bat or bird may snap one up now and then for its minerals. Their strange makeup is valuable to makers of magical devices. They are said to go into the timeglass of the mage, and also into fine smoke powder and dust of illusion. Some whisper that a great free city's priceless oracles are crystalmist colonies imprisoned forever by powerful magic.