Splinters of Daoloth

Those who enter the Sacred Light (an avatar of Daoloth) become aware that it is a living, alien presence. At first, the person experiences euphoria, but as the subject’s mind fills with knowledge, terror follows as this knowledge mounts and mounts, becoming too much for their mind to bear. Unless finding some way to stop the process, the acquisition of cosmic truths may turn this person into a Splinter of Daoloth.

Yuggs

Yuggs are large, aquatic, pale grey worm-like creatures up to four feet in diameter and twelve or more feet in length. Yuggs have a large, round sucker-mouth similar to a lamprey or hagfish. This mouth contains several rows of hornlike teeth and is surrounded by six small tentacles six inches to two feet in length. Like snails, they leave stinking trails of slime behind them.

Death-Vines of Xiclotl

Large, carnivorous, intelligent, purple flowers with tentacles. They are able to launch their seeds with enough force to reach space, and subsequently land upon distant worlds throughout the galaxy.

Vile Fungus

The Vile Fungus appears to be a mass of regular mushrooms from a glance, yet they can cast out tendrils that can infect those they touch. The victim is then progressively overcome by the fungus until they are unable to move and the cycle starts over.

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.

Space Eaters

The Space Eaters' description is a little vague, but I believe they are just a single column of blinding light that can send out spiralling tendrils into the brain of its victim.

Reptile People

Reptilian quadrupeds that predated the arrival of man, the Reptile People are now extinct, though their bodies are perfectly preserved within the catacombs of Irem, City of Pillars.

Spawn of Nyogtha

The Spawn of Nyogtha are the offspring of blasphemous unions between humans, ghouls, and Nyogtha. The children produced by these matings degenerate into shapeless abominations after about three decades. Until this stage they easily pass as human, though they have viscous, black ichor running through their veins, so a medical examination could give them away. Once transformed, however, their torso and limbs have a bloated corpulence, yet the monstrous form maintains skeletal hands and face, though with hideously distorted features, razor-sharp talons, lupine fangs, and bulging eyes with hellish crimson orbs.

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.

Servants of Gla’aki

When someone is poisoned by Gla'aki, they become his undead slave, though still able to perform individual actions. At first they can still pass as their former self, but as time goes on, they become more corpse-like.

Devil Creepers

A Devil Creeper's (previously call Hell-Plants) seeds are planted within a human host. When ready, the plant sprouts violently from their body, killing them in the process. The plants themselves are huge, covered in bulging eyeballs and fanged, lipless mouths.

Thralls of Cthulhu

Once human worshipers of Cthulhu, they chose to partake in rituals that transform them into bloated, grey shadows of their former selves, with vestigial tentacles around their mouth (or head). In return, they are given immortality.

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.

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.