Shoggoth was a massive amoeba-like creature made out of iridescent black slime, with multiple eyes "floating" on the surface. They are described as "protoplasmic", lacking any default body shape and instead being able to form limbs and organs at will.
Creatures in a ritual to conjure up creepy tentacle creatures to help fight their battles. These creatures might hurt them as much as they help. The Mushslugs don't fully trust and are apprehensive about the entire endeavor.