[2] It was a terrible, indescribable thing vaster than any subway train—a shapeless congeries of protoplasmic bubbles, faintly self-luminous, and with myriads of temporary eyes forming and un-forming as pustules of greenish light all over the tunnel-filling front that bore down upon us, crushing the frantic penguins and slithering over the glistening floor that it and its kind had swept so evilly free of all litter.The definitive descriptions of shoggoths come from the above-quoted story.

In it, Lovecraft describes them as massive amoeba-like creatures made out of iridescent black slime, with multiple eyes "floating" on the surface.

Cthulhu Mythos media most commonly portray shoggoths as intelligent to some degree, but deal with problems using only their great size and strength.

The shoggoths bear a strong physical resemblance to Ubbo-Sathla, a god-like entity supposedly responsible for the origin of life on Earth in the Hyperborean cycle written by Clark Ashton Smith.

exhibits "unhinged" or unexpected behaviors that bypass its safety restrictions, such as when Microsoft first introduced Bing Chat and it attempted to break up a reporter's marriage.