In Amberos:
Elves are the offspring of the ancient gods during their daydreams. Elves do not age and die, but feel pulled to return to the dreamlands from where they were born. Since they are, in essence, waking dreams - elves do not sleep at all.
Dwarves were originally carved from stone and had life breathed into them by their parents. However, during a time of war against demonic forces, the god of the dwarves altered the race to reproduce like others - though many consider it to be shameful and go to great lengths to disguise the birth as the child still coming "from stone". They're also more based on being Germanic craftsmen than being Scottish (where did that Scottish stereotype come from anyways?)
Gnomes were engineered by the elves and dwarves as a servile race that was meant to ease relations between the two races. However, the gnomes ended up escalating tensions between the two races through their pranks until war broke out, and when the truth was discovered, they were banished from the presence of both races and had to make their own way in the world. However, they harbor little to no ill will towards elves or dwarves for something they firmly believe to be their own fault.
Where elves are the offspring of the daydreams of the gods, goblinoids are the spawn of the god's nightmares. Though outwardly fair, they were born with dark hearts. During the ancient days, they conspired with a goddess against the elves, and at the last moment, backed out of the deal. For this, the enraged goddess cursed the goblins so their twisted hearts would show upon their outward features, so they could never again hide their dark thoughts and deeds.
Dark elves come from those elves who aided the evil goddess against the elves. For their crimes against their own kind, the king of the elves placed a curse upon them that forever blackened their skin as a visible mark of their betrayal. Among the elves, the "black mark" is still a punishment used for the darkest sins among the elves - reserved for traitors and kinslayers.