Orb Angel:

Orb angels are fairly low-ranking and low-level servitors of the gods. They are part of a sort of "super-species" of creatures known as "Angels" who as a whole have devoted their existence to serving the gods.

Though angels differ from type to type, orb angels are useful but fairly weak, so much so that they are literally the least physically powerful angels, servants who serve and aid gods and who can be summoned without considerable difficulty by faithful mortals. Some types of gods have forces composed of almost exclusively orb angels.

Their primary functions are reconnaissance, espionage, and data-gathering. They possess the ability to defend themselves, but their defensive capabilities are weak in comparison to their other abilities so they don't do well as warriors or assassins.

Orb angels tend to be seen favorably by gods of knowledge, politics, espionage, and exploration. When they are left without gods to serve they tend to serve higher level and higher-ranking angels as scouts, spies, and note-takers.

When left to their own devices they tend to be research topics related to the gods and they tend to congregate near holy sites.

Interestingly enough they are not the most common angel type, despite being the least physically powerful.

Theoretically, it could be possible for an orb angel to evolve into another type of angel, but the biggest factor in determining angelic evolution is the will of the angels themselves. Unlike nearly every other kind of creature that can evolve, if an orb angel can evolve what sort of angel they evolve into depends on their divine master.

Common House Mouse:

Mice are tiny rodents, who can be found in the wild or in communities of humanoids. Mice can be useful to the right kinds of humanoids in a variety of ways so there are plenty of people who have begun to carefully and deliberately breed mice.

Mice are common familiars for spell-casters and for spy-masters who use magic to remotely infiltrate enemy strongholds or capital cities. Mice are also easily mutatable, possessing a small body and a creative genetic code that can easily be altered by skilled scientists, flesh-shapers, and others with an interest in genetics, templates, and mutations.

When awakened mice can evolve into fascinating humanoid creatures including but not limited to mice-people and werehumanoids, animals that can transform into humanoid form. When left unawakened mice can evolve into greater rodents such as psionic or elemental rodents.

Orc:

Orcs are waring humanoids fond of battle and bloodshed. They are incredibly adaptable and can mutate spontaneously, unlike most other humanoids.

Orcs are just a bit bigger than humans, are at least as skilled in both hunting and forging metal weapons, armor, and tools. Though orcs can farm, they prefer to engage in bloody action and combat to secure food. They are one of the few humanoids considered to be "civilized" by some while also engaging in the consumption of both other kinds of humanoids and their own kind.

In the distant past, orcs were taught that only battle and bloodshed matters by their ancient deities, including the long-forgotten creator of all orcs. As a species this is a belief they took to heart and maintain to this day, though plenty of exceptions to this grandest of rules exist.

Orcs can be primitive or civilized. They can be kind and considerate or brutal and degenerate. They can be the best of neighbors or brutal and subjugative tyrants. But most are brutal, war-mongering creatures.

Entire tribes of orcs have been conscripted into the armies of powerful dark lords in the past, and they have served dark overlords, ranging from powerful witches and warlocks to martially gifted warlords eagerly, even slavishly. Many orcs yearn for that once again: to be united in service to a powerful and brutal lord of shadows who unifies their species and throws them into battle against the forces of justice.

Orcs can be evolved or "devolved" depending on a variety of circumstances which is one of the reasons why they are sought out by cruel warlords who seek to use them as part of grand, conquering armies.

Physically overwhelming orcs can be forcibly "devolved" into less intelligent but more physically powerful creatures, particularly ogres, whereas smarter or more ruthless orcs can be evolved into a range of brutal humanoids from the half-orc half-extraplanar monsters known as Dark-Drinkers to the more conventional elemental and magical variants that commonly exist across most creatures that are capable of evolution.

Sentinel Demon:

Sentinel demons are a physically imposing sort of demon with a unique connection to the plane known as the Heart of Darkness.

These demons tend to be less intelligent than many of their fellow demons yet they possess an innate connection to their home plane that allows them to call upon the plane to mark their enemies, mark territory, and even change the way layers of the plane look. They are the uncelebrated architects of cities within the Heart of Darkness.

These dim-witted demons aren't especially hard for chaotic evil creatures to get along with, provided they are allowed chances to inflict violence on other creatures and can eat the corpses of their prey, despite it being unnecessary for them to do so. They are well-suited to work as guardians or as hunters.

Sentinel demons tend to be solitary creatures and though a large number of them exist, as they are lesser in power than other "intermediate" demons, their territory within their home dimension tends to be isolated.

Sentinel demons can evolve into other forms of demons. What they evolve into depends in large part on what sort of personalities they had and what sort of harm they liked to inflict while living as Sentinel demons. Like all other extraplanars, not all Sentinel demons want to evolve or see the purpose of evolving. Sentinels who see no purpose in evolution for a long enough time gain the "true" template, marking them as members of their species who are embodiments of Sentinel demonhood.

Brutal, sexual sentinel demons can become unusually cruel incubi or succubi, bestial sentinel demons can become a variety of brutal demonic predators such as vulture demons, bear-like Korachtures, or demon dogs.

Magically oriented sentinel demons can become filth demons or other variations of more common types of demons. Sentinel demons who used armor and/or weapons can become more brutal, warlike types of demons from individually powerful champions to teamwork-oriented raiders who operate best in roving packs.

Poisonous Subterranean Frog:

PSF's are a common type of frog found in forests and other temperate environments.

These are toxic frogs with the ability to poison and paralyze other living creatures who try to prey on them. These are also somewhat common familiars used by spell-slingers of all sorts and even magically inclined assassins. As a species, the PSFs appear to be the product of artificial selection.

These are poisonous frogs who spend significant portions of their lives underground. Like the Common House Mouse, they have separate evolutionary paths depending on whether or not they are awakened prior to their evolution.

Awakened PSFs as a whole tend to walk the great frog evolutionary path. The great frog path leads to a variety of humanoid forms, some of whom are nearly indistinguishable from humans but with natural abilities related to poison.

Unawakened PSFs as a whole have access to a wider variety of evolutionary paths, most of which take multiple evolutions before they can become even remotely humanoid in shape. That said there's plenty of diversity in this path, including access to incredibly poisonous forms of frog, forms of frog that are well-suited to life underground, and that are capable of demonstrating magical or psionic powers.

Great Frogs:

Rare evolutions to a wide variety of frogs, great frogs are the evolved versions of frogs who were awakened and thus made more humanoid in their thinking and habits.

These creatures are almost universally familiars to druids or spell-slingers fascinated by poison.

Great Frogs possess a variety of powers related to poison and toxins. They can be trained into skilled assassins or adept healers who can offer skilled treatment related to poisons.

Great Frogs can serve as skillful gladiators or as handy aides to rangers.

They can evolve into a range of humanoid creatures with abilities related to poisons and who can handle lesser frogs.

Tree Wolves:

Tree wolves are a rare sort of evolved wolf that is well suited to life in forests. They are adept climbers, capable of limited bursts of wind magic, and have intelligence that is similar to an awakened lesser wolf.

These wolves are physically weaker than other evolutions accessible to wolves, but their flexibility and natural skill within their arboreal domains are second to none.

These wolves tend to get along well with druids and other appreciators of nature. They can often act as stewards of a forest and can aid humanoids who treat them with respect.

Tree wolves are evolved from grey wolves. Grey wolves can evolve into a variety of lupine beasts if left unawakened. When awakened they can evolve into Cu-Siths, creatures which are a cross between humanoids and wolves, or they can evolve into werehumanoids like awakened mice can.

Tree wolves are one of the few animals that, under the right circumstances can begin to evolve into nature spirits. Otherwise, tree wolves begin to evolve into true elemental animals, creatures in the shape of animals but who are composed of elements.

Forest Bears:

Forest bears are large predators who lurk in forests and who hunt down all sorts of forest life. They are one of the few predators in non-magical forests who hunt down other predators as much as they hunt down prey.

They are thickly muscled creatures who are difficult to kill in one on one battles. Even trained guards and professional soldiers can lose a fight to a forest bear if they don't take it seriously.

Forest bears are easily influenced by magic and often serve greater forest spirits as either awakened guardians or as charmed cannon fodder.

Awakened forest bears evolve into berserkers, a rare form of humanoid who possesses the power to invoke a bear's strength into their physical might. They look like orcs, but are generally considerably more passive and less predatory than orcs are unless they are continually attacked by other humanoids.

Unawakened bears tend to become bigger, more monstrous creatures as opposed to becoming a different sort of bear, which is rare among animals. Creatures that evolve from bears tend to be overwhelmingly large creatures with powerful jaws and natural armor. It's not uncommon for humanoids to track bears and eliminate ones that are nearing evolution when they come across them, so as to prevent them from evolving into dangerous and wild monsters.

True Devils:

True-devils are a powerful species of devils, inhabitants of the dark plane known as Infernius. Devils can take on a multitude of forms, and most are not "true-devils". So-called "true-devils" are unique creatures who have powerful abilities, including the ability to command devils who exist along the traditional "hierarchy of Infernius".

Any and all arch-devils are true-devils. But not all true-devils are arch-devils, in fact at any one time, the maximum number of arch-devils capable of existing is a mere 9. True devils are incapable of evolving, as they are the final form of devils.

Each true devil has unique powers and abilities that are decided upon by their souls. A true devil is the penultimate devilish authority and every single true devil has at least a few devilish followers. The only devils higher up than true-devils are the various members of devilish nobility who rule out of massive devilish palaces, attended by devils of all sorts. At the top of the hierarchy of devilish nobility, are the powerhouses known as the archdevils.

Imps:

Imps represent the second-lowest rung on the ladder that is the devilish hierarchy, occupying a position significantly higher than that of a mere soul-orb. They are ambitious, craven creatures with attitudes that make it clear they desire to be near power.

Physically they represent a strange mixture between humanoids with odd skin tones and winged scorpions. They have the tail and wings of a winged humanoid while their basic body shape is that of a weirdly colored human.

They have legitimate magical power, but it's not good enough for the creatures to defend themselves from greater creatures, so they tend to teach magic-users in mortal worlds about basic magic and serve them as errand-doers, while steadily pulling them towards legal evil.

Imps are the first real devils. They are significantly above soul-orbs in terms of power and potential. Eventually, an imp could proceed all the way up the normal hierarchy of devils and end up at the top rung of that particular ladder as a Vizier devil, Infernius's greatest standard devilish inhabitants, but under normal circumstances, such an ascension could take tens of thousands of years.

Other evolutionary pathways exist, including an imp choosing to become a "true imp" and therefore staying an imp forever but gaining considerable power and influence within the impish community, or imps becoming variant creatures of other sorts when sufficiently mutated.

Half-Devils:

To call half-devils a species is tricky but for the purpose of codifying them they will be classified as such. Half-devils are creatures who have a fiendish parent and a non-fiendish parent. Their powers and appearance are dependent on their parents.

Half-devils tend to be dark creatures, who are fanatically loyal to the hierarchy of Infernius and upon their deaths many of them become devils themselves. Particularly powerful half-devils instantly become the same type of devil as their devilish parent, which is thought to be the origin of assorted scary stories in mortal worlds that warn children not to indiscriminately murder supposedly evil creatures. Half-demons also exist, and there are a multitude of different kinds of "half"-extraplanars.

Half-devils lean strongly towards classes that enable them to influence others, and thus many of them are spell-singers, clerics, paladins, and politicians. Not all of them are evil so some become great heroes, but devils who come across uncorrupted half-devils take great pains to corrupt them.

Half-devils tend to be the most effective ambassadors from Infernius to the mortal worlds. Some of the more powerful half-devils are children of the ancient arch-devils, unaging ambassadors busy on distant worlds, schmoozing with kings, presidents, and other world leaders to lead them to corruption and Infernius. These half-devils have overcome mortality and owe their unending existences to a variety of sources.

Half-devils are among the few creatures who can't evolve. In exchange for that their bodies are well-suited to immortality and becoming immortal for them is far easier than it is for humans or other types of humanoids.

Floating Skulls:

Floating skulls are secretary-like undead creatures that float alongside and provide aid to either dungeon lords or skilled necromancers.

These are evolutionarily dead undead that exists to perform administration tasks that other undead are not suited to doing. These undead beings are capable of performing a variety of tasks that are useful for self-care or for doing tasks that other creatures may find boring.

These creatures are magically capable of flight, speech, and even basic creation or teleportation if their masters are sufficiently powerful. They can activate traps, speak on behalf of their masters, or even "attack" on their own, though they are useless as fighters since their attacks pass harmlessly through any creatures they fight. In exchange for that most attacks harmlessly pass through them as well.

The secret to the creation and near invulnerability of these odd creatures is that they are a mixture of construct and undead, not pure undead beings like skeletons, or pure constructs like golems.

Soul-Orbs:

Soul orbs are the weakest and dumbest creatures on the infernal hierarchy. These incorporeal creatures are the purest remains of bits of evil souls that have been melted down and reformed.

They are the only sort of devil that can naturally evolve into the next rung on the devilish hierarchy though they can also be automatically promoted to higher rungs along the infernal hierarchy by sufficiently powerful true-devils or arch-devils.

These orbs are barely alive and automatically obey commands issued by any true-devil. They are generally used as promotion fodder to create more advanced devils or are used as surprisingly powerful bombs by wicked true-devils.

To command one, it merely takes a true-devil willing it to attempt a task. Many devilish dungeons demand the ability to command soul-orbs to even enter, which is why throughout infernius devilish dungeons remain inhabited and unlooted.

Soul orbs are capable of exploding and depending on the sort of explosion may be able to force themselves to reform, but oftentimes the explosion's effects are permanent.

Soul orbs are one of the few types of extraplanar that can be awakened. Unlike other awakenable creatures, the evolutionary pathways accessible to soul orbs are not influenced by whether or not they are awakened.

Mummies:

Mummies are somewhere between lesser and greater undead, existing in a weird sort of intermediate state between two power levels.

Mummies are undead creatures who when they are found as actual existent beings are the corpses of former nobility possessed by greed and hate so powerful it clings to a sort of unlife.

But oftentimes mummies found in the wild are the result of leftover greed slowly coalescing into an unholy and nightmarish monster capable of inflicting dreadful wounds that cause those hit by them to bleed humility and happiness instead of blood.

Mummies possess powerful claws that can easily tear apart metal armor. Real ones made from corpses could often inflict curses on enemies that were easy for evil creatures to shrug off but harder for good creatures to resist.

Mummies can be created magically and oftentimes they are found as magical creatures composed of shadow stuff and not actual, physical creatures.

Dark Unicorn:

Dark unicorns are a demonic corruption of powerful celestial creatures known to mortals as Unicorns. Their celestial counterparts are famous for their kindness, dignity, mercy, and hope, but Dark unicorns are lustful creatures who are the dark embodiments of the fury at the heart of a stampede and the belligerent pride of a mighty lion. Their horns are potent magical items that can be used as part of deadly magical rituals or as the foundation of sinister weapons. That said acquiring a Dark unicorn's horn is a foolhardy task as the Dark unicorn will fight hunters seeking their horns to the death.

Dark unicorns can be made to serve wholly evil creatures as steeds or even as prized pets but will refuse to serve anyone else, even deities. Dark unicorns are brutal slave traders who can lure in a variety of creatures using their majestic appearances and then stunning them with a variety of powers so that they can be contained, restrained, and sold into slavery.

Dark unicorns evolve into fiends, what sort of fiend depends specifically on their alignment and age. Dark unicorns are among the only creatures who can evolve into the creatures who predate modern demons, but clash with demons in the deeper, darker layers of the Heart of Darkness. This makes them prized by those ancient, dark creatures who seek to ensure that they evolve into the demon's ancestors.

Dark Elves:

Dark Elves are corrupt and powerful Elves who live in underground cities and in the ancient past worshiped powerful lords of darkness.

In the ancient past, Dark Elves lived in communities with institutions that upheld sinister matriarchies where women had absolute control. Now, even without the backing of mighty lords of darkness women continue to be the more dominant sex but things are considerably more egalitarian and it is possible for men to be deemed equals in smaller communities of the hedonistic creatures.

Dark Elven communities are built on the backs of other, physically mightier creatures who the Dark Elves lord over, through usages of their impressive magic. Their willing allies include gigantic and darkly beautiful arthropods and a variety of species they created through orgiastic breeding experiments that included forcing humanoids and animals alike to breed with demons.

Given Dark Elves' proclivity to worship and serve lords of darkness it's possible there is an Althos shaped hole in Dark Elven society that might be worth attempting to fill. But if that is an objective you decide to pursue it's important to remember that as a species Dark Elves are ambitious, bloodthirsty, and zealous beings who equate power and violence. Their worship would be dark, violent, and sinful, and gaining their worship would likely require many acts of darkness.

If Dark Elves are made to evolve they most likely would evolve into a range of hybrids that combine the power and aesthetics of dark elves with the power of the monsters lurking in the World Beneath the World. Mating between the two is possible and has resulted in a range of successful hybrids like driders and a range of beautiful yet impossibly cruel monsters.

Goblins:

Goblins are among the smallest and cruelest humanoids people commonly encounter. They are dangerous, bloodthirsty pests and very few, very remote tribes still worship idols and totems. This makes them one of the few sapient creatures to cling to faith.

Most goblins though have begun to modernize, bit by bit, and have joined greater civilizations as members of a sort of servitor caste. Many goblins have forgotten about their bloodthirsty roots but retain their cruelty in new and often innovate ways.

Goblins are one of the few "super-species" that can be found in many mortal worlds. Goblins evolve into fiercer, larger vaguely goblin-like creatures if they live long enough and gain enough experience to do so. The larger creatures they evolve into are powerful and domineering, but they are thankfully rare.

Goblins who live in "nondiscriminatory" communities of humanoids are closely watched and encouraged to not gain the experience needed to evolve. If they evolve anyway they are often chased out of the communities they were once welcome in, which gives them cause to tap into their innately aggressive and domineering attitudes.

Filth Demon:

Filth demons are corruptive and mutative oozes who can shape-shift and are fond of corrupting nature as well as ruining social bonds. They are skilled but deeply troubling creatures who can pollute water, devour crops, and generally make life worse for humanoids and animals alike.

These cruel critters delight in ruining nature and in doing things that turn creatures, families, and friends on each other. Their abilities are often specialized in that direction, not just actively ruining nature with their poisons but inciting betrayal and violence among those who were exposed to their toxins.

Filth demons can evolve into a range of more sly demons. They can easily become the humanoid-demons known as succubi or the equally humanoid but more forthright incubi. They can become the temptation demons known as the Cabras, demons whose forms resemble a mixture between humanoids and goats. They can also become more social but monstrous-looking demons, or even demons specializing in poisons and in the destruction of structures depending on how they affected the world around them.

Bioluminescent Mushrooms:

These gigantic fungi are a standard and common form of fungal life encountered throughout the World Beneath the World. They are especially common in entrances to and exits from the World Beneath the World where they are planted to lure surface dwellers into the darkness of the W.B.T.W.

These are pretty standard massive fungi. Their purpose is to light up and they do spectacularly.

Some of these mushrooms can defend themselves by spraying things with invasive spores that can penetrate the skin and grow into a mutant variant of the standard mushrooms while killing whatever wandered too close, but a range of creatures in the W.B.T.W. have skin that can't be penetrated by the spores.

The most often unintentional way that spores of bioluminescent mushrooms reach new places is when the mushrooms are high up in a cave or tunnel and release spores onto people who don't see them. Those spores can be taken for kilometers on the clothing of whoever they hit, before flying off of them due to a breeze and landing in new, fertile soil or on a newly deceased corpse to feed on.

These creatures don't commonly evolve, but they can evolve. It's just not common for them to do so, due to their stationary nature. The few bioluminescent mushrooms that manage to evolve, evolve into outstanding fungal creatures. Most standard fungi who can pull off an evolution evolve into truly spectacular things.

Most bioluminescent mushrooms that pull off an evolution evolve into fungal folks, fungi who superficially resemble humanoids and who are capable of creating weapons, tools, and social societies that are eerily and deceptively similar to those of humanoids. If under the command of a malign intellect this could become a deadly trap that results in these fungal societies rapidly expanding.

Sometimes bioluminescent mushrooms evolve into other, more aggressive fungal forms such as gigantic, walking fungi, who can feed on living creatures and corpses alike to increase in biomass and produce kilograms of spores.

Perhaps most rarely of all the glowing mushrooms evolve into unusual animal forms, like spiders, scorpions, birds, or fish and gain access to new places to plant spores. These new forms most often appear whenever an intelligent takes control of the bioluminescent mushroom and commands it to behave in a particular way.