Puffer

Floating dormant in the void between worlds, a puffer is a smooth, taut sphere with no features at all, anywhere from about 20 to 40 feet wide depending on how long it has slept. Up close its skin is clearly not stone, which sets it apart from any asteroid. Once it wakes, it takes on a shape somewhere between crocodile and scorpion: a jaw full of sharp fangs and a venomous tail arched over its back, able to strike in any direction.

A puffer only fights when active. Dormant, it can be killed by anyone who reaches it out in the void, and its carcass then makes a valuable store of air. Touching more than a ton of air wakes it instantly.

Its bite deals 1d12 damage and its stinger 1d6, and anyone stung must make a saving throw vs. poison or die.

For most of its life a puffer drifts through the cold, lightless reaches beyond the outermost planets. It moves by letting out a thin stream of air, far slower than any starhelm, yet it senses ships and other large objects up to 100 miles away. It creeps toward one and, if it can reach it, lands and comes alive. It has enough air for 5 to 10 landing attempts; if all fail it dies in space without breeding.

A puffer lands only once. It must kill a creature to serve as a host for its eggs, lays them, then drifts back into the void to die. Three to four weeks later 1d100 tiny, already active puffers hatch (hp 1 each, AC 10, THAC0 19). Their stings are just as deadly as an adult's, and each hunts a warm-blooded animal to sting to death. A hatchling that succeeds eats its kill and grows fast, then slowly draws in air until it becomes a dormant ball 30 to 40 feet across. With a puff it launches itself into the void, at well below starhelm speed, to spend years or decades adrift.

Puffers eat meat and prefer prey of human size or larger. They can grow and breed on smaller animals, but need many of them to match one good 150-200 pound body. A drop from space to a full-sized planet would kill one, and its air jets are too weak to lift it off a world, so puffers keep to ships, asteroids and other small bodies in space.