Humans
Despite being the rarest peoples, humans are actually believed to have been the first race on Terra. Humans are extremely sensitive to radiation and are the weakest, shortest-lived, and least magically-inclined of Terra's four great races, but they are the most intelligent and the most dextrous. Humans possess opposable, multi-jointed digits on either end of their arms, capable of using delicate machinery, playing a variety of instruments, and manually cleaning the insides of their ears and noses. Using these digits, humans have invented a variety of tools and devices to assist them in these and other labors.
◈ Rot-touched humans are a subspecies of human, who are not born mutants, but have had their genes mutated through direct exposure to very high amounts of radiation very quickly. They are ageless, require no water, and despite a popular myth that states otherwise, can be killed through conventional means. They resemble living corpses and are slowly deteriorated by direct sunlight, leading many to seek shelter underground.
◈ Halfbeasts are the unholy spawn of humans and beastfolk. They usually resemble humans with scant animal features, such as tails, ears, or wings. Some see them and find them attractive, others see them and picture their sinful parents copulating. Whatever the case may be, they are rarer than humans and are frequently performers in circuses and exotic clubs. The only colony of halfbeasts are the mermaids, who are pretty absent in the affairs of non-mermaids.
Beastfolk
The beastfolk are the most diverse, and perhaps most loosely organized of the four great races. Whether or not the beastfolk are the oldest race in Terra is largely a one-sided debate between the beastfolk, who submit the notion that the beastfolk are Terra's oldest race, and the rest of the world, who favor the tangible, much older records of humanity in the debate. In spite of this, the beastfolk are generally a proud, bull-headed people, depending on their exact species. To be fair, the most bull-headed of them are the bullmen.
◈ Plantfolk, while not "beasts", exist all the same. They have a lot of in-fighting and rivalries only they are able to remember and differentiate, such as a bitter, long-standing racial hatred between leekfolk and radishfolk. Because of their integral bond with nature, many live in harsh, isolated regions.
◈ The fishfolk, also colloquially called The Awful Fishfolk, are the most widely-hated subspecies on Terra. There is no one reason, but a slew of factors that go into this -- They reek, no matter the breed of fish, speak in a language only they can speak, and they steal things. They steal like it is going out of fashion, right in front of you if they have to. They also cannibalize their dead almost immediately.
Greens
The Greens -- Orcs, Ogres, Trolls, Hobgoblins, Goblins, Ghouls, and all manner of nefarious hoopajoops -- are a universally tusked, pointy-eared, viridescent peoples. Some are small and quick, such as those in the goblin families, whereas others, such as the ogres and orcs, are large and muscled. Because their appearances are so widely varying, many members of other races, such as mutant humans and particularly stout lizardfolk, are often mistaken for Greens and discriminated as such. The Greens evolved from humans who have adapted to high levels of radiation.
◈ Sky goblins, despite their name, are not goblins and cannot fly. Their short tails make them imps, and while they cannot fly in the true sense, they can jump the same distances, proportionately, as a flea. Their wide, padded feet help them glide as they fall downward and kick at prey with their powerful legs. They eat mostly birds, young harpies, and other sky goblins.
◈ While commonly believed to be members of the extinct Dwarf race, tappers are the most common subspecies of troll. They can be distinguished from dwarves and trolls alike by their dark green skin and gray beards. Many signal to one another when they sense cave-ins by tapping their single, long index finger on the cave walls, which gives them their name.
Elves
Where the beastfolk were made brash and dim-witted by the radiation, and the greens made hideous and deformed, the Elves were given what they call "Elfspeak" -- The ability to communicate ideas to other living beings psychically. Because of the use of telepathy and psychic empathy is so widespread in their cultures, they generally almost never speak. <Elves sound like this> While powerful wizards and other elves can shut off their minds to Elfspeech, humans, beastfolk, and greens cannot.
<As you can imagine, this does not help their popularity>
◈ Forest elves are the elves most attuned to Elfspeech, and are said to have invented it. They lack mouths, instead communicating entirely with their minds, photosynthesizing in order to give themselves nutrients when necessary. Some say they can use Elfspeech to communicate with trees, though they aren't keen about discussing the matter with non forest elves.
◈ High elves, as their name would suggest, are the tallest of the elves. They are known for their impressive fortresses and a lesser known facet of Elfspeech known as Elflistening, where they are made privy to the thoughts and emotions of others. Most use this for political scheming and other underhanded means.
