The Cacogens

The mysterious Cacogen Elves living on the Green Moon of the Orbis have been a global-scale boogieman among all sentient races for thousands of years, even if they died out millennia ago. This is because on a date every schoolchild knows, 4 Astionel, in 14988BCE, the Cacogens pulled a comet out of its orbit and smashed it into the capital of the homeland of their enemies on the Orbis, the Lin Elves. This ended the Second Elven War and very nearly ended life on the planet; the impact cracked the mantle of the world and left much of the western Great Continent uninhabitable for more than a thousand years.
Understandably, in the 27,000+ years since then, no one has bothered them.

Basic Information

Anatomy

Cacogen Elves, if they still exist, would preserve the lineage of the Lin Elves, who were eradicated in the comet strike, but whose closest relatives are the Dovalni forest elves living near the same region today. Presumably the Cacogens were tall, slender, and more cerebral than athletic in build; the split that occured between Lin and Cacogen was said to go back to racial as well as cultural differences, with the Lin elves' skin cast more in shades of yellow or gold, and the Cacogens more in gray or silver. It's true that the Deep Elves, who were also an offshoot of the Lin Elves from the first Elven war, have silvery and occasionally fairly light skin, but culturally and socially the splits were separated by thousands of years and totally different motivations. It is unlikely that the Deep elves really have much else in common with the Cacogens other than some overlap in the extremes of their skin tones.

Genetics and Reproduction

Presumably as the Dovalni today, with a very long gestation period, with reproduction otherwise proceeding in the usual way.

Growth Rate & Stages

The Dovalni have a lifespan of six to ten centuries, and slow aging; Likewise the Pilaani elves, though they do age about twice as fast, nevertheless retain their health and good looks well into the 400 - 600 year range. In both cases puberty and reaching of adulthood proceeds at about the same speed as in humans, but the aging process of the body once it reaches adulthood takes much longer.

Ecology and Habitats

Vertalluna, the green and blue moon of the Orbis, seems to be a temperate forest punctuated by thousands of scattered lakes and swamps rather than a world of active plate tectonics, with continents and oceans in the fashion of the Orbis. Whether the elves control/once controlled the climate, or this is a natural phenomenon, is not known. On account of being over 300,000 miles through the hard vacuum of space to reach, accurate information about life on its surface is almost entirely speculation. The moon is not quite tide-locked to the Orbis but it revolves more slowly, and lacks an appreciable tilt on its axis, which wizards and scholars speculate accounts for its lack of seasonal color change. The trees, if they are trees, are green year-round.

Additional Information

Perception and Sensory Capabilities

Presumably they were like the other species of Elves in that they retain excellent vision in the dark, a preternatural agility, and a kinship for magical things; if they were able to escape as a race to the moon, and to bring a comet down on the heads of their enemies, clearly they had more than a normal aptitude for spellcasting.

Civilization and Culture

Average Technological Level

Interplanetary travel, though presumably by magical, not mechanical means.

History

The Cacogen Elves emerged as a separate splinter from the Lin Elves some years after the first Elven War, when the Gray elves were defeated and driven underground to become the Deep Elves or Drow of the Orbis today; These were distinct from the non-religious Arcane or Moon elves who were pushed aside more and more after the Sun elves and their Gods did so much to win the first Elven war. As time passed, the Moon elves became more and more atheistic, and found themselves more and more isolated from the rest of the society on the basis of their pursuit of arcane magic. For them, this was in opposition to the divine magic of the Lin Elves, who clung to their gods, and these Gods clearly favored the Sun Elven types over the Moon elves - to be clear, this was not only a physical but also a cultural separation, and "Moon Elves" still exist among the Dovalni.
The Moon Elves of that time soon entered into open fighting against the Sun Elven faction of the Lin Elves, and were banished; taking this as a boon rather than a punishment, they went a step further and not only left the Pronoan Heartland but left the planet entirely. The Lin Elves, however, were powerful enough to continue to harry their splinter, godless enemies by the conjuration of demons and monsters on the Moon who killed without the slightest discretion. Eventually, the Cacogens had had enough of the Lin Elves, and of the Orbis entirely.
Whatever Gods the Lin Elves worshiped were lost when that race was erased from existence by a Cacogen-aimed comet that blasted into Lin and completely through the mantle of the planet, not only erasing the Lin homelands in an instant, but altering the geography and even the geology of more than half the world. The Orbis was plunged into a global firestorm and darkness that lasted for years, wiping out the majority of life on the planet. It would be millennia before the Elves or the other Races could come out of their caves and eat something other than mushrooms, cave crawfish or each other, and millennia more before something like civilization would once again arise.

Origin/Ancestry

Cacogen Elves, like all sentients, are descended from some mixture of the Ur-species - the Gazafi, the Aeldvolk, and the Hyinchneumon. Elves generally and Cacogens specifically are a 414 mix - one part Aeld for every four parts Gazaf and Hyinch.