Pencil; going to offer you a slight retcon mulligan because of mechanics. If you want, you can shift all those undead to the Undersea, just because you can't spread them without another fauna token to parasitise, and you can reach the Lightseen from there. Or the Kaos Chasm, which is also legit. Heck, even on the plains where everything just died is cool too.
The Gem Mite (Crystal, Pioneer) - A tiny crystalline being. It resembles a small fleck of a gem with tiny legs and mandibles. Created by a god that loves beauty, they consume not food or energy, but rather beauty itself. They prey on the gems in the walls of the caverns. Attaching themselves to the gems, they extract the shine, luster, and color of the gem. The mites body takes on the aspect of the gem that was just consumed, and can grow larger if the gem was of high enough equality and size itself (relative to the number of mites that were feeding on it of course). When the mite becomes large enough it splits in two down one of it's fracture lines, becoming two new mites, who then go off to consume more beauty. This unnatural consumption of a gem leaves it as a small grey stone, as it's beauty is sucked away. However a gem will eventually recover from this, although it can take years or decades. Only the beauty of the stone was sucked away, with the cause of the beauty, that being the composition of the gem, still intact eventually the beauty will grow back, shining out from the gem and returning color and shine to it.
Variants:
Solar crystal mite: A offshoot of the Gem Mite, this being has learned how to feed on the beauty and shine of light itself! They appear as (when visible) a translucent gem mite with a spark of light within. They slowly drain light from the vicinity around them. When a colony of these beings moves into an area the brightness of the area slowly decreases, eventually plunging the patch into perpetual unnatural darkness, from which the mites then migrate from looking for brighter pastures. Areas effected by this will then proceed to grow brighter over time, eventually coming back to their full natural light.
Sea Mite: A offshoot of the Gem Mite, this being has learned how to feed on the beauty and clarity of water. Hard to see in the water, they appear as clear or light blue gem mites. They slowly drain the clarity and purity of the water around themselves. When a colony of these beings moves into an area the clarity of the area slowly decreases, eventually turning that area of sea into a murky morass of unidentifiable and non existent particulate, from which the mites then migrate from looking for clearer pastures. Areas effected by this will then proceed to grow clearer over time, eventually clearing back to their natural state.
The Weaver (Crystal, Tier 1) - A small spider like creature, with a rocky hard body and flexible legs, it lives on the ocean floor among patches of Blade Grass. It constructs structures made of blade grass, using it's rock hard body to avoid being cut. The structures it creates are large weaving, complex three dimensional patterns, at key points in the weave it attaches small rocks from the sea floor, and when the structures are finally finished being created the stones entwined within absorb the blade grass that they are attached too and are born as new weavers. The weavers otherwise take no substance, and survive purely on the energy raised by their birthing ritual, and thus lead quite short lives before they eventually deanimate into simply a rock and a few rotting stands of grass. In places where bladegrass is rare weavers are solitary creatures and will defend their patches from one another, but in places where it is abundant they will gather together in colonies and work together to create truly grand weaving, sometimes ones that take multiple generations to make.
Variants:
Constructor: This offshoot of the weaver has learned to use the beauty of the gem mite to fuel their reproduction ritual. They appear as a normal weaver, but instead of long thin legs of grass, they have short wide legs of crystal. They use their heavier limbs to smash gem mites, which they then bulldozer together into piles, that they flatten and press together to make shining plates on the ground. The weaver seeds are placed on the plates, and their shining magnificence eventually gives birth to a new batch of weavers.
The Sirens (Crystal, Tier 2) - Sirens are split into two subspecies, and the species as a whole is prone to many mutations, often having a extra claw, or one less claw, being smaller or bigger, having a weird number of eyes or many other flaws are very common. They can mate with one another across subspecies lines. The first one represents a massive stone crab, which lives into the weavers nests. It absorbs the inspiration seeded within the stones of the nests, stopping them from ever becoming Weavers, but allowing the crab to full it's purpose, which is to create music. After absorbing a weaver seed it is able to compose a song, which it then sings out across the sea. This is how the Sirens communicate with each other, and find mates.
The second subspecies looks a lot like the first, but it has many webbed feather like structures growing from it, this, along with a lower body density, allows it to swim though the sea. These Sirens prey on the Cha Chas, using their feathers to disguise themselves as fellow Cha Chas looking for a mate in order to get close enough to kill them with a snap of their claws. From there they pluck the bodies and make nests of the feathers. Surrounding themselves in large colorful nests, carefully arranged in certain patterns, is how they attract mates.
Sirens typically live in small colonies, normally one Alpha, which has the biggest nest or the most beautiful song, and a few betas, which generally follow it's orders. In areas where there are both weavers and Cha Chas there are sometimes mixed species nests, which can have two Alphas. Despite their abilities to compose sometimes quite complex songs, they have no other intellectual capacity, and appear to sing purely on instinct.
They have a limited lifespan, as their flaws cause them to slowly crumble away most of the time (although there is a very large variance in the time this takes, some of them die immediately after birth, and some can rarely last hundreds of years). They will also slow down and eventually deanimate if they are unable to find weavers or Cha Chas to steal inspiration from. It's not totally sure why exactly they need this inspiration to live.
The Bowlmen (Crystal, Tier 3) - The Bowlmen resemble squat humanoids, with short thick bodies, attached directly to a squarish head. They have long and thick legs and arms ending in clumsy digits. Their most distinct feature is the large stone bowl attached directly to their head. They instinctively gather materials from the grove that they live in, mainly the Haze Bees, to produce various mixes inside of their bowls to produce a staggering variety of chemicals. After a chemical is produced they consume it and store it internally for later use. They use these chemicals for almost everything in their life, consuming them for energy, using them to ward off the stings of the bees though a miasma of smoke, releasing clouds of poison for defense. They even communicate with each other by releasing various chemical markers. The bowlmen typically live in small groups. Despite their alchemical powers, they are still of animal intellect, only creating and using the chemicals on instinct with no true understanding of what they do.
Variant: Aquamen - A offshoot of the bowl men, their bodies have greatly changed to adapt to their new home. The main body is a large oblong mass of low density stone, the limbs have adapted to water, becoming wide paddles that it uses to swim though the water. The head has shifted somewhat to face in the correct direction. The bowl has changed most of all, moving along with the head shift, it's merged to the back and become much larger, in addition it's grown a thin retractable crystal covering. The being refills this structure with air at the surface, allowing it to stay descended in the water for hours at a time if need be.
The Unmakers (Crystal, Tier 4) - The Unmakers are, at their core, a shard of crystal empowered with a divine spark. They gather up the materials around them to produce their bodies, which offers a staggering verity of possible shapes and sizes, although most tend towards a sleek and stealthy build. The purpose of the unmakers is the hunt. They search out beings of higher complexity, and after killing them, absorb them into their own mass, from there the beings are reduced down into their base components, flesh beings into carbon and water, crystal or rock beings into the inanimate rocks that they sprung from. In this way they turn the complexity of the creature into energy for themselves, which they use to power their life, any excess energy going to growing their heart crystal. The heart crystal will eventually split when it reaches the correct size, turning into two or more unmakers. The unmakers strictly live alone, and will refuse to share territory with one another, fighting to the death for it if need be.
The Gem Licker (Animal, Tier 1) - Small, four legged lizard-like creatures with long, thin tongues that dwell in the dark. They are blind, born without eyes and prey on the Gem Mites, catching them on their sticky tongue and gobbling them up. Their skin is dull, the colour of bare rock. Extinct.
The Cha Cha (Animal, Tier 1) - A sea dwelling bird that a foot big. They lack beaks and use flat teeth to chew the blade grass near their home. They also seem to enjoy ramming Atmotes, causing them to bust. No one know why.
Haze Bees (Animal, Tier 2) - A dog-sized bees of red hue, these insects chew on Archen Runners, using them for both food and nest material. Their sting, used in defense of the hive, has a hallucinogenic effect on their attacker. Some unfortunate attackers are so badly affected by the venom they sit in a haze while the bees continue their assault, eventually being killed by venom overload.
Purple Bat (Animal, Tier 3) - These fly capable mammals navigate the darkness by ultrasound. Their sharp claws will dig in to the place that Beneficial Eyeshrooms have taken root and pull them out before taking it back to their nest and eating it. The brutal removal of the eyeshroom tend to leave the former host dazed and confused, but no deaths from the action has been recorded aside from ones with other factors compounded on.
Sparkings (Fire, Pioneer) - Tiny wisps and sparks of animate flame. These pseudo creatures feed off the ambient heat in their terrain, splitting into fresh sparks when they are sufficiently fed.
Magma Crabs (Fire, Tier 1) - Only vaguely resembling a crab, these six legged creatures have thick shells of rock taken from their volcanic surroundings. They feed off the concentrated heat of sparkings, which nourish their innards of liquid fire.
Dragon (Fire, Tier 2) - Two of the six legs of the magma crab have mutated into wing-like appendages, and these dog-sized creatures have pointed snouts that make them resemble lizards. Their skin is covered in steel scales from the iron in the surrounding environment, and their flesh is now primarily stone, with veins and organs of liquid flame, as well as a pouch in their belly from which they can eject fire from their mouths while hunting. They feed primarily on magma crabs, sustaining their inner fire from their tasty liquid innards.
Variants: Abyssal Dragons; a species that feeds on the sugary roots of firegourds.
Fire Eaters (Fire, Tier 3) - Appearing to be living flames scouring the landscape for food, the fire eater actually has a thin layer of ash that serves as a skin, and fine ash-built organs that are invisible against the blazing light of its inner fire. Fire Eaters feed by passing over and through other creatures and sucking out the heat and flame from them, leaving them icy, charred husks or empty frozen shells. They reproduce by splitting in two when sufficiently engorged.
Echoes (Fire, Tier 4) - Titanic in scale and appearance, these massive linkages of obsidian mirrors, lenses and focusing crystals shift and swirl around a magnificent core of raging fire, manipulating the light and heat for locomotion and to create powerful beams by which to hunt and smelt new mirrors and lenses for their offspring. In addition to feeding on lesser forms, the echoes specifically hunt fire eaters to consume and remake their inner flames into the animating force for the echo offspring.
Nomadic Moulds (Fungi, Tier 1) - Sedentary and asexual in its mature form, the spores of the Nomadic Mould only germinate when it lands upon a non-fungal organism. Upon doing so, mycorrhiza sprout into the creature's skin, allowing the mould the ability to colonise areas farther away than its parent. The mould derives nutrients from the creature until it reaches maturity, at which the it detaches itself from the host and plops itself into the ground, beginning the life cycle anew.
Firegourds (Fungi, Tier 1) - Resembling a vase in shape, they are composed of a hardy carapace suited to the hellish landscapes of the Kaos Chasm. It filter feeds on Sparklings, converting excess energy into a sugary liquid, which is stored in stubby mycellium-roots. Energy-rich, these roots also adhere the Firegourds to the surface.
Pirate Tethers (Fungi, Tier 1) - Colonial fungi that grow on Atmotes. They instinctively grow in shapes that make the Atmote more aerodynamic, aiding their mobility. They also produce spiky stems to wars off predators. Feed on the Atmote host via specialised needle-mycellium that uses an anaesthetic to prevent combustion.
Beneficial Eyeshroom (Fungi, Tier 2) - The spores of the eyeshroom germinate under two conditions: landing on a gem or landing on an organism. Landing on a gem produces a short-lived fungi that releases more spores before expiring. If it lands on an organism however, the fungi quickly moves through the organism's body and latches onto the eyes (if present. If not, it simply infests and kills the host before releasing spores). It then consumes the eyes. using anesthetic so the host is usually not aware due to the lack of pain and lack of much light in the caverns. The empty eye holes are then grown into, sprouting wide-capped but short-stalked mushrooms that neatly fits into the hole. They glow an iridescent colour and can be used by the host as eyes. In short, the Eyeshroom replaces the host's eyes with eyes capable of vision within the darkness of the caverns at the cost of nutrients being siphoned by the fungi.
Blade Grass (Plant, Pioneer) - Blade Grass grows on most types of terrain, being a hardy, resilient plant, useful for seeding plant life. it has incredibly sharp blades, and cuts those that stray to near towards it. There is an aquatic variant that grows in the shallows, where light from above is plentiful.
Variant: The savanna variant of this sharp-edged plant is tougher and larger, holding more nutrients because of the lower amount of rainfall. It is a dusty-yellow color. Otherwise, it is the same as the original Blade Grass.
Archen Runners (Plant, Tier 1) - A plant that uses runners to reproduce. It has bright red but highly toxic fruit, which also hold the fruit inside, killing creatures that would dare to intrude on the privacy of their territories. It has a light lime stalk, and grows to about 3 meters on height, morphing into a tree like shape by the end of it's lifespan, which is about 90 years.
Archen Sapling (Plant, Tier 2) - Akin to the archen runners, the archen sapling grows taller, has thin wooden bark to support its structure and splits at its crown to produce several red fruit-bearing branches. It no longer reproduces via runners but exclusively by fruit.
Walking Snares (Plant, Tier 3) - These plants have the ability to walk slowly, hence the name, changing position taking hours instead of minutes. Migration therefore occurs while the seasons pass, snares moving as dark shadows on the plain, too slowly for any faster adjusted eye. They also change position locally to get into the best position for sunlight and prey, though they have to remain rooted to the ground regularly, and can only uproot for short amounts of time.
Verna (Plant, Tier 4) - The Verna are a quiet, plant-like humanoid race, their god having uplifted them from their slow thoughts to quick. Almost too quick. The Verna hide among the grass, and are around a meter in height, though some few rarely reach almost two. They still use photosynthesis to generate energy, but catch large game to support their primitive minds.
Deathweed (Undead, Pioneer) - This plant has a unhealthy dark purple colour on it's stem and leaves. It typically grows in cracks and in-between plants of greater size. However, it experiences a dramatic increase in growth when near a dead body, the plant growing all over the corpse and competing against other rival weeds. It can also slowly leech energy from other plants, latching a stem into the bark or sinuous plant material of neighbouring flora and sucking the sap from it.
Ghoul-Bats (Undead, Tier 1) - These creatures are heralds of coming sickness. Their bodies are generally quite wrinkly and a greyish-pink color. Their teeth are yellowed and are covered by huge amounts of bacteria. The bat typically bites the victim, then waits for the bacteria to take it's toll before striking again, this time to kill. They can be seen flying in great flocks overhead, covering the sky and blotting out the sun like a great stain on the sky.
Vector of Death (Undead, Tier 2) - A parasitic creature, these pink lumps can be found growing in multitudes on the backs on unintelligent creatures, slowly leeching the life and energy out of the host, turning it from what it once was into a husk of it's former self, before devouring it with minuscule mouths as it dies. They reproduce by laying eggs in the host, which burst out upon the death of the host, and have root like appendages which hold them onto the surface of the host.
Atmotes (Sky, Pioneer) - Tiny organic balloons, clusters of Atmotes drift the atmosphere. A single eye adorns their top. They try to protect themselves from predators by pressuring themselves and they explode harmfully if punctured.
Blue-callers (Sky, Tier 1) - Resembling four winged, four legged birds, they drift in the air currents. Their heads are coated with eyes, looking in a ll directions. On their body, they have a fanged mouth.
Variants: Red-callers; a species with red plumage that prefers higher altitudes.