Chthonians

Chthonians are giant burrowing worms—though not as large as Dholes—with tentacles for a "head". They are telepathic and can create earthquakes at will.

Children of the Wind

The Children of the Wind are bloated, corpse-like monstrosities, with stumps for limbs. They are always accompanied by howling, gale-force winds.

Chaugnar Faugn, Brothers of

Brothers of Chaugnar Faugn

The Brothers of Chaugnar Faugn—both lesser and greater—are simply smaller versions of him.

Chakota

The Chakota is a six-foot-tall worm-like mass of sickly purple-veined muscle covered in dozens of human faces that weep, shout, and cry out with great woeful feeling.

Byakhee

Described as "not altogether crows, nor moles, nor buzzards, nor ants, nor vampire bats, nor decomposed human beings," I've yet to actually see a Byakhee portrayed with all of those features. Because they were also said to be "tame, trained," they are generally treated as the mounts of the Mythos. So much so that they are often referred to as star-steeds.

Blighted Ones

Blighted Ones are humans who have succumbed to a fungal parasite. From the moment of infection, they have mere days before the fungus takes control of their bodies. 

Atlach-Nacha, Daughters of

Daughters of Atlach-Nacha

The Daughters of Atlach-Nacha begin as normal women who have been chosen by the Great Old One to become one of its giant spider companions. Eventually, The Chosen undergoes a horrific transformation, shedding her human skin, and changing into an enormous spider. This spider is almost completely black, except for the swollen, pulsing abdomen that is streaked with green and gold.