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.

Great Race of Yith (New)

In prehistoric Australia, the technologically advanced Yithians were attacked by the Flying Polyps. In order to escape, the Yithians transferred their minds far into the future. Unheroically, they traded places with a race of hive-minded insects, leaving them (undoubtedly confused) in the Yithians' old bodies in the midst of the Flying Polyp war, never to be heard of again.

Great Race of Yith

The Great Race of Yith—also known as Yithians—are a race that swap minds with other races throughout time and space in an effort to learn everything they can about the universe. The most famous of their inhabited forms are the conical beings of Earth's prehistoric past. The swapped mind subsequently inhabits the Yithian's body until they return, jotting down all they know of the home for the Yithians' great libraries.

Spawn of Yig

The Spawn of Yig are the offspring of Yig and a human, and take on the characteristics of both parents. Skin is scaly and coloured similarly to that of a snake, while limbs are shrunken and dangle uselessly from the body. The face is partially human, but the eyes are cold and lidless.

Inhabitants of Yekub

The worm-like Yekubians send special cubes out into space, and if an intelligent creature finds and looks into the cube, their mind is switched with the Yekubian's for a brief time.  

Beings from Xiclotl

The Beings of Xiclotl look like 16-foot high metallic trees, and are enslaved by the Shan as brute labourers.

Travelers

Much like the Shan, Travelers invade a host's brain and take control of them. Unlike the Shan, however, Travelers are physical beings, and enter their victim's body through their mouth. They start off in a larval form (shown below) and mature once inside the host. Unlike the Shan, however, Travelers can't easily vacate their host.

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.

Hounds of Tindalos

The Hounds of Tindalos live in the distant past, when life was still single-celled. They have the ability to use the angles of the world as portals, travelling through both time and space. If a person becomes known to a Hound, it will hunt them relentlessly.

Shugoran

The Shugoran race look like smaller versions of Nyarlathotep's Shugoran form. They are amphibious and have black, catfish-like hides, with small wings—or fins—and long proboscises.

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.

Proto-Shoggoths

A Proto-Shoggoth is basically a Shoggoth made of human flesh and parts, which it can create and remove at will. They are not true Shoggoths, however, but creatures created through alien science or arcane secrets. Smaller Proto-Shoggoths may even take human shape and move undetected amongst them.

Petesouchi

Petesouchi start life as regular humans, but after adolescence, begin to change into a large crocodile, though retaining their human mind. Like Deep Ones, not all Petesouchi make the change, while others may only partially do so.

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.

Fosterlings of the Old Ones

The Fosterlings of the Old Ones are the mutant offspring of matings with human females and Outer Gods or Great Old Ones. Through a special ritual, the deity sends a dream which reaches into the womb of a pregnant woman, altering the genetic structure of the unborn foetus. Once born, the child spends many years as a regular human until one day transforming into something more closely resembling its alien parent. This change occurs in a single evening.

Nioth-Korghai

Nioth-Korghai appear octopus-like, but are in fact a dark-orange, "bundle of fungoid creepers joined together at one end"—so essentially tentacles without a body.

Nagäae

Nagäae have toad-like, transparent bodies, their pulsating innards covered only by a thin layer of leathery skin. They have the hind legs of a frog, and four forelegs of a man. Their face consists mainly of bulging eyes and an oversized mouth with two forked tongues. They are amphibious, found all around the world, and serve Cyaegha, sharing their sire's malevolence.