Bast

Bast—or Bastet—is the Egyptian Cat Goddess, typically appearing as a woman with a cat's head, though she can appear as a regular person or a regular cat (large or small) as well.

Children of Yog-Sothoth

The Children of Yog-Sothoth—previously Sons of...— are the result of Yog-Sothoth mating with a human female. The most famous of these progeny are Wilbur Whately and his twin brother from The Dunwich Horror, in which instance one was born as a mutated human while the other was a giant, invisible monstrosity.

Typhonian Beasts

Typhonian Beasts are avatars of the Egyptian god Set, and can take the form of a jackal-like beast, or human with the beast's head.

Tindalosian Hybrids

Tindalosian Hybrids look like living Cubist paintings. They generally try to maintain their human form, but their image often wavers and ripples. By ingesting a bit of the blue ichor left behind by a Hound of Tindalos, a human may become infected and mutate into a Tindalosian hybrid. Certain spells or elixirs may produce the same effect.

Lords of Tindalos

The Lords of Tindalos are wolf-like creatures that appear to not be wholly of our dimension, their shape constantly shifting and changing in angular pieces. They have the ability to travel through the angles of the world to any other angle in time and space.

Shoggoth Lords

Smaller, more intelligent Shoggoths that are able to mimic humans in both speech and appearance... albeit grossly obese and hairless.

Shoggoths

Shoggoths are possibly Lovecraft's most popular non-deity monsters. They have amorphous forms and are nigh on unkillable.

Denizens of S’glhuo

The Denizens of S’glhuo are beings composed of sound, though they appear thin and tall, with huge pupilless eyes, and a skin covered with tiny, rippling blue scales. Their fingers are boneless.

Rat People

Once human, Rat People have degenerated to a near animal state. I get the impression from their write-up in the old Malleus Monstrorum that they are even less human than those pictured below, as it says that they sometimes walk on all fours and has no mention of weapons or even clothing.

Spawn of Othuyeg

The Spawn of Othuyeg are simply smaller versions of their sire, meaning they are a mass of white tentacles surrounding a single eye... so basically a white version of Cyaegha (hence the usurped image).

Minions of Othuum

Minions of Othuum are yet another "heap of twisting, ropey tentacles". It's become pretty clear to me that peoples' association of Lovecraft and tentacles didn't actually originate from his writings at all, but instead, those that came after him.

Ghoul Hounds of Leng

Ghoul Hounds of Leng are based on the beast from the Lovecraft story "The Hound". They are large, bat-winged canines. They relentlessly hunts down anyone who steals amulets of their likeness.

Courtiers of the King in Yellow

Courtiers of the King in Yellow (previously called Pallid Dancers) are dressed in tattered yellow rags like the King in Yellow and wear pale masks, dancing with the grace and rhythm of both a ballerina and a whirling dervish.

Gyaa-Yothn

Gyaa-Yothn are said to be related to—and are possibly just domesticated—Ghasts, though they have a horn protruding from their head and are covered in fur. They are ridden by the people of K'n-yan, as well as being used as beasts of burden.

Gn’icht’Tyaacht

The Gn’icht’Tyaacht are tree spirits native to the jungles of West Africa, and are only able to leave their Nuwanda Trees at night. They are seven-foot tall, lanky humanoids with long pointed heads. They also have huge claws and prominent, sharply pointed teeth.

Ghasts

Ghasts are repulsive beings which shun the light. They leap on long hind legs and have yellowish red eyes. Ghasts have an excellent sense of smell and their face is curiously human despite the absence of a nose, a forehead, and other particulars. They speak in coughing gutturals.

Formless Spawn

Formless Spawn (previously "...of Tsathoggua") seem to be like mini Shoggoths, though they can only alter their shape, not create organs etc.

Dholes

Dholes are basically giant worms. And I do mean giant. They are the largest creature in the Malleus Monstrorum, including deities. It's said that there are none on Earth, which can only be a good thing, because they burrow through the ground, infesting the entire planet until it is destroyed.

Desh

The Desh are creatures from an alternate dimension that can be summoned to earth through the brain of a sentient being. They come in many different shapes and sizes, two samples of which are pictured below, named Lesser and Greater Desh. Lesser desh appear as large silvery tadpoles with limp, toothless mouths, and with a row of dark, bead-like eyes across their narrow heads. Their long limbs are tough and springy. Greater desh have slim, fish-like bodies with four long limbs knotted with cords of stringy muscle. Wide mouths bristle with curved, six-inch teeth. The top of the sleek head is crowned with a bundle of 2 to 8 lidless, plate-shaped eyes arranged in a crescent.

Star-spawn of Cthulhu

Cthulhu's spawn are basically just smaller versions of himself. Some were trapped in R'lyeh when it sank, though many were not.