Art by Steve Purcell.
These black, protean beings may be found in deep sunless caverns, often acting as guardians and protectors of secrets. They may accompany or herald the arrival of a Great Old One or stand in the god's stead, or simply lie motionless for years at a time, like some quiet dark pool waiting to be disturbed by the unwary. Whether they are born of a specific entity or magically created is unknown.
Formless Spawns can change their form and shape in an instant, from toad-like lumps to elongated things with hundreds of rudimentary legs — to any conceivable form. Being a living viscous liquid, they can ooze through small cracks, usually finding a way through any obstacle, while also able to cast spells, and can form vocal organs to issue strange sounds — no record exist suggesting they have ever communicated with words a human could understand.
Like Shoggoths, they can shapeshift both to take various forms and to shape appendages to suit their needs for accomplishing their master's bidding and attack their targets in nearly every conceivable way. They are surprisingly flexible and plastic, and can quickly flow into a room through the tiniest of cracks. They attack by trampling their targets, biting them, or crushing them with their grasp.