Source: Dreams of the Yellow King, pg(s). 82
A formless spawn at rest resembles a simple puddle of dark, thick liquid. It is capable of assuming any basic shape but incapable of holding that form for long. It attacks with whipping, writhing pseudopods, blocking combat manoeuvres. A formless spawn is capable of covering a 15-foot-diameter pool to a depth of a foot, and it weighs just over 9,000 pounds. It is as dense as oil and can float on water, unless if it actively swims down.
Formless spawn are physically disinclined to stay in one configuration (doing so nauseates the formless spawn) and mentally incapable of even comprehending the concept of a fixed form. They often ridicule those who they view as locked into a single shape, although they rarely can be bothered to speak, for formless spawn consider talking to food a waste of time. Contrary to some legends, formless spawn are never able to hold a single shape for extended periods of time: these are often accounts of shoggoths that have developed this capability.
Formless spawn are ageless and sexless, all of them having spawned from sources deep below the ground. The original formless spawn issued fully formed and aware from Tsathoggua himself, but after a time, the rocks near where he slumbered seemed to become capable of creating them. When a formless spawn masquerades as a simple pool, its metabolism slows significantly and it can stay for centuries without eating, but upon awakening, it is always ravenous and risks starving to death if it cannot find food.
Most formless spawn serve as temple guardians or agents of Tsathoggua's cult, to the point of being called formless spawn of Tsathoggua. They often reside within carved containers that appear as little more than decoration within Tsathoggua's temples. Wild formless spawn have either lost their temples or survived the destruction of a cult that they once served, and wander the Darklands relentlessly, driven by an urge to seek out new cults or temples to serve. Some formless spawn, almost always clerics, end up becoming leaders of Tsathoggua's cults themselves.