In my sci-fantasy world where things are similar to our irl modern tech level and civilisational structure, i have this sentient dinosaur species that are two legged, slightly shorter than humans, with whiskers, fuzzy feathers and more usable 4 fingered trex arms. Ive been trying to get their appearance right and might post abt them here later.

But basically they are pure carnivores and domesticated humans thousands of years ago when they had their own biopunk interstellar civilisation and when their civilisation fell, partially due to humans, the ones stuck on the main Earth analogue planet, Enia, just did their own thing until they merged with the rising human civilisation. Nowadays they just live among the humans in parallel societies.

For unique quirks, they are fully carnivorous like i said and like humans have a lot of quirks from being once arboreal endurance predators built for the savannah, these guys are once snow leopard type alpine hunters turned steppe endurance predators. They very rarely get motion or altitude sickness or vertigo and their sense of balance and navigation is insane, plus they can see in the UV spectrum. They also have this intense need to be in open spaces and cold areas, not necessarily claustrophobia or extreme heat sensitivity but a type of depression when these requirements arent met for years on end. They also sometimes feel the need during certain stages in their life related to what used to be signals for ancient breeding seasons, to abandon their friends and family, travel and settle down in a new place as soon as possible and find entirely new friends.

They also have intense bouts of mania and obsession around completing tasks associated with lack of nutrients from living in omnivorous human societies. They need more iron, calcium, and stuff like that and cant eat too much of spicy or acidic foods like fruits. When these dietary needs arent met, they get these manias that can quickly lead to delusions and violent outbursts. Basically modern life sucks for them but ig it does for everyone else too...

I've made a handful - Mine were created for games so they have unique traits designed for a game system in mind.

One I made are a slime-ish people called Tarbies. They don't naturally have bones so they find/construct their own, they can crack and split in icy weather so they don't live in the cold, and they are born/buried in giant pools where their memories all sort of melt together.

(That last part is a significant problem which they are constantly dealing with)

They're really physically dense and hard to wound unless you hit an internal organ.

They naturally tend to copy people/animals/things that they find interesting which generally creeps people out - This also leads them to being exploited for labor or menial jobs as other races might pretend something is interesting to trick a Tarby into skillfully copying and completing tasks.

Narratively they were designed to be a parallel-ish-design to the setting's robots but alien to just about everyone else.

I have a concept I'm not sure what to do with: The Cordyceps Symbiote.

It's essentially a slime mold that can interfere with its host organism's endocrine and neural systems. Its lifecycle encourages it to keep its host alive as long as possible, so it evolves a mutually beneficial relationship with its host organism. The primordial symbiote organism could adapt relatively rapidly, so soon after it evolves (evolutionarily speaking), most organisms on the planet have a corresponding symbiote organism.

One host species evolves specialized structures that allow its symbiote to grow complex neural structures, allowing it to evolve complicated group behaviors like large social groups, pack hunting, animal husbandry, agriculture, and eventually writing. This species pair quickly becomes the dominant species (pair) on the planet, similar to humans' position on earth.

The host species also develops the ability for abstract thought at a similar pace with its symbiote, as each increasingly complicated instruction needs to be understood by the host. However, the symbiote is generally has far more influence on its host, via endocrine and neural signaling, than the host has on the symbiote.

Recent medical advances have made it possible for host organisms to live without a symbiote, and while synthetic symbiote hosts are a promising area of research, no viable solution exists for a symbiote to live without a host.

I've come up with a few, but I'll just talk about my favorite race in my world.

There is a small continent (Tah) located in the tropical/subtropical zone of my planet where the only humanoids are a turtle-based race known as the Tahween. They are known for their slow movements, long lifespan (average life expectancy is 340 Sun Cycles, which are roughly equivalent to years, but consist of ten 44-day "months"), and wisdom. They are extremely hostile to outsiders, and very few of them ever leave their home continent. Those who do choose to leave are forbidden from returning. While they are not very good at physical combat, their wisdom allows them to harness powerful water magic and earth magic to defend their homeland. Luckily, they do not use this magic for wars of aggression, since they are isolationist and do not wish to expand their territory/sphere of influence.

Their government is entirely based on who is the strongest wizard. If you want to be the Lord Wizard, you must defeat the current one to get the throne. If the Lord Wizard dies of natural causes/accident without being defeated, a tournament is held to determine who gets the throne. Their economy is basically what we would call perfect communism on Earth. Everyone contributes what they can, and everyone receives what they need. Their diet mostly consists of leaves and fruits, they will occasionally eat a small animal if the opportunity presents itself, but they don't actively seek out meat. The concept of marriage is entirely foreign to them, they do not form romantic bonds. During their mating season, it's basically a free for all. They are known to mate with multiple partners during each Vibrancy (their equivalent of our "Spring"), and they often choose an entirely different set of mating partners every Sun Cycle.

As far as religion/mythos, they believe that Tah Ara (similar to Gaia, the spirit of the planet) created them from water, leaves, soil, and a bit of magic. They abhor physical violence, as they feel it is disrespectful to Tah Ara's creation. As far as the afterlife, that's not something they buy into. They believe that the materials/energy that make up an individual are not inherently theirs, and are recycled to create new life. They have no concept of a soul, a Heaven, or a Hell.

Their staunch isolationism is a result of an attempted invasion by the Thaug (a humanoid, Rhinoceros-based race, think Rocksteady from TMNT) that took place 2408 Sun Cycles ago. The Thaug are an aggressive Imperialist race, who seek to control as much territory as possible, and only respect power. That invasion/war led to a third of all Tahween being killed or captured, but in the end, they were able to repel the invading force. As a result, the Tahween take a similar stance as the Sentinelese do on Earth, "stay the heck away from us or we will kill you before you can manage to say "hello".

According to my lore, a couple of species were picked up with the migratory fleet that ended up in the remote world that is my current setting. Since landing, starting a mega-terraforming project, and the collapse of both the galactic civililization as a whole, and of the local variety, what's left of each species is more or less in survival mode.

Of the 4, there are humans, spread out among the many lands and islands of the world.

The Vabvva, a moth-like race that no-one has h#ard from since tge collapse, as they were the only ones capable of breathing the miasma that covers the lower altitudes.

The other 2 races have since formed a symbiotic relatiinship and are called the Rru & Tarryu. While within their secluded homeland, the small Lizards half of the species run things, but the wolf-like Tarryu people run things while within their nomadic ships, as the Rru are needed to run their Storm Engines.

Other Sapient apecies have begun to emerge, many since the Great Collapse. Human once, they've under several transformations to become what they are today, namely Chimerics.

Chimerics generally fall into 2 catagories, those that seem to have maintained some semblance of what made them people, and the Dire, who are little more than beasts. Of those still welcome in polite society, there are the Nephlan, the Tephjan, and the Vaizan.

The Nephlan are varied in appearance, but tend to be shorter in stature and have rough, scaled hides that resemble a pengolin. They are quite resistant to the wayward energies of the world.

The Tephjan are often referred to as 'Harpies', but are quite varied in their bird-like appearances. Many tend to fued with themselves based on whichever type of bird groups they belong to, but are usually quite welcome in ports and on ships that sail between the islands.

The Vaizon never leave their Forest-home, making them quite like elves in that regard, but with an extreme amount of various animal features that they seem to be able to change at a whim. They have an almost unnerving determination to serve their deity, Fuengthyrith'ta. Literally: She Whose Eyes Beheld the Stars, the being who enabled the creation of all chimerics through a ritual that the Vaizon oversee and enforce,

That's the main ones, anyway. The setting lets me create new chimerics as needed, each leaning between Dire and civilized based on how disruptive they are to their immediate environment.

In my world, wood elves, of buried within a year in a grove, become a part of it (sorta like in Speaker for the Dead) and high elves choose to enact this ritual living separately.

These majestic trees grow to great heights, akin to redwoods. When such a tree dies of old age, the heartwood animates but has only the vaguest memory of its prior lives. That's the origin of warforged for my world. Incredibly rare, filled with history but oddly disconnected from it.

Haven't invented new races yet, only twists on existing ones.

Lizardfolk? Eat their dead with reverence, carve their stories onto their bones and then reanimate then for labor or battle. Their dead never truly die and remain a respected part of their culture.

Dwarves care about achieving immortality through craftsmanship, humans through magic. It's only halflings, and gnomes to a lesser extent, that have simply accepted death and lived their lives.

In my heavily homebrewed version of Greyhawk I reworked most of the non-human species. I wanted them to behave and feel similar to their traditional versions but come up with some actual biological and cultural reasons for their behaviour rather than using the overly simplistic D&D alignments (which I don't use at all).

Elves' emotions change very slowly and need long, sustained experiences to really trigger them. But when triggered they also last much longer, sending them into weeks or months or years long emotional states (love, sorrow, rage, etc). This means that fleeting events have almost no emotional impact on them, which makes them seem cold, aloof and in some cases cruel by human standards (e.g. single moments of violence inflicted to them or by them register no emotional response). Their culture has extremely intricate customs of etiquette and behaviour to manage a society of what are essentially sociopaths in their day-to-day lives. Elven armies have corps of elves that are in the midst of long-term rage (often triggered by the impacts of the war) that are essentially in a months long berzerker state.

Orcs are no less intelligent than humans but have very poor long term memories, so they aren't good at tasks that require extended study and building up of knowledge. But this means they live very much in the moment giving them powerful insight and wisdom, their perception and thoughts on what is currently happening aren't influenced by biases and expectations. They have very high pain tolerance and casual violence is an inherent part of any discussion or debate among them, they express their thoughts and feelings in inherently physical ways. They breed very quickly which leads to regular expansion and conflict amongst themselves and as they expand into new areas.

And there's a whole thing with goblins that after I'd put it together someone pointed out to me that it is almost literally the xenomorph aliens from the Alien franchise (goblin queens giving birth to huge litters, goblin births picking up genetic material from what the queen has eaten so if she eats humans they get hobgoblins, etc). They have a hyper pack mentality, where the bigger the group they are in the more energetic and stupid they are. So a single goblin creeping around will be terrified of everything, but a big swarm of goblins will be suicidaly reckless. They also have photographic memories for navigating their huge cave and tunnel systems, which makes them good at learning and copying stuff (though they aren't good at inventing new stuff). The pack mentality lessens over time as they age, so leaders are usually older goblins that can think more clearly, but also a lot of older goblins leave the hive to make their own way in the world.