Alright. Getting some mixed signals on the drow/Fishthul situation, so how about a lore dump!
Primer on the Dark Beings:
At the beginning of creation there were magics of life and death, both accessible through wizardry and sorcery, but they were separate, and rare was the being who could effectively use both. This changed when the Dread Giant Durkim awoke from his slumber about eleven thousand years ago.
When Durkim went to sleep, the world was a beautiful and empty place of ice and dust. He was more than a little enraged to find that while he was out his fellow giants were slain and creation had occurred, blotching his perfect world with teeming life and irregularity. Durkim wished to challenge creation, but knew he could not do so alone, and with the remaining true giants little more than vegetative sperm banks used to sire heroes of men, he had to find help elsewhere.
Rending heaven and earth, Durkim created a field of darkness that would allow him to easily create, maintain, and re-animate followers. Those attuned to the field of darkness would never hunger, rarely tire, and could command life and death as a single school of magic. The minds of those attuned, however, are tainted by Durkim's hatred of life and civilization, and as such so called 'dark beings' are universally but not irresistibly drawn to crimes against life, happiness, and common decency.
Durkim, of course, was defeated and slain, but his body was torn asunder by his followers and buried all around the world, so that his field of darkness might still blanket the planet in his absence. Today the Dark Beings are seen my most as monsters and trouble makers, but no longer as essential threats to creation.
Orcs: The original servants of Durkim, Orcs are green or grey skinned humanoids with prominent jaws and underbite. The stand in at 7-8 feet tall. Orcs exist today as the remaining aspect of Durkim's will; They exist solely to destroy all life not attuned to the Dark Field, and to serve any sleeping giant who might rise in the future, and only the strongest of magics can draw an Orcs mind away from these goals. This is not to say Orcs are mindless; They can form friendships and make alliances, and are generally considered the second to only the diggers in technology and second to only the fey in magic. To them, a non-hostile non-orc is something to be manipulated into conflict with other life, befriended and attuned to the dark field via ritual, and/or tricked into aiding in the production of furies.
The continued threat of violence and seduction of other life by the Orcs following Durkim's death was the prime reason that the Pantheon of Four was formed and the diggers were created. Too virtuous to corrupt, and too industrious to defeat, your people drove Orc Kind to near extinction. In this age, the only remaining orcs can be found far below the earth, waging war with the very deepest of drugar civilizations. On and close to the surface, many still fear Orcish Burial Temples, which scholars believe are command by sentient mummies still loyal to the Orcish cause, waiting in vast numbers for the right moment to rise again.
Goblins: Goblins are green, grey, or orange skinned male humanoids. Standard goblin peons (typically just refered to as goblins unless speaking about the race overall in highly accurate terms) have disproportionately large heads. Hobgoblins have similar proportions to those of a human. A goblins size varies depending on the task he was created for. A Hobgoblin stands between five and six feet tall. Hobgoblins and Goblins are biologically the same creature, and the differences between them are a matter of how they are sired and raised.
Standard goblins are created as mostly functional 'adults' with basic knowledge of language, weapon use, and the skills required for menial labor. They learn slowly, and suffer from an almost total lack of free will, which makes them easy to control - they will not follow their dark urges if commanded not to. Hobgoblins are created as infants, and allowed to experience a childhood of 2-12 years before reaching maturity. A Hobgoblin allowed a full childhood is easily smarter than the average digger commoner, but still prone to loyalty and able to keep its dark urges in check for the good of its master if allowed in outlet, which usually takes the form of abusing the peons.
Goblins were first designed by the diggers who would go on to become the first Drugar. Ironically their purpose was to combat the orcs, who had been chased far underground and to other places where food was hard to come by. The given justification for dabbling in the Dark Field was that Diggers could never finish off the hungerless orcs unless they had hungerless laborers and soldiers to match. The Drugar toleration of Hobgoblin cruelty among their ranks, however, was seen as rephrehensible by many, and served as one of several driving forces behind the division of the digger races.
Today Goblins are most commonly captive bred in dark fortresses; structures geometrically designed to amplify the dark field and make the goblin creation process far less taxing to those preforming it. Most are in the service of Drugar, but some belong to the drow in spite of the fact that the demonic drow pantheon finds the bodies and souls of those tainted by the dark field to be poor eating. Although dwarves cannot stand Hobgoblins and typically kill such wicked creatures on sight, it is not unheard of for dwarven civilizations to keep and employ any peons they capture from the Drugar.
Furies: Furies are the most powerful creatures attuned to the Dark Field, and can be born when a sin is committed between two sentient beings; One attuned to the field and one not. The sin that births a Furry is often (but not always) sexual in nature, as the spark of life is inherently present in the act. The most well known and common flavor of Fury is the Bugbear; The formula to create one is well known, they are born with the power and skill to spawn goblins, but are otherwise sterile and unable to sire troublesome nightmares or trolls. Tempering the dark urges of a sentient Fury is nearly impossible, so aside from Bugbears birthed to spawn goblins in chains or monsters made to fight alongside the orcish hordes, they are rarely created or even tolerated by civilized folk. In the wild, Bugbears and other Furies lead nasty tribes of trolls or feral goblins.
Non-sentient and bestial furies are far more common. Many animal breeders know the secret to create furies that appear as particularly large and intelligent hungerless equines and canines, and human kings are fond of keeping massive furies that imitate the forms of the dragons they worship. These bestial furies, although far more beligerant than a domestic animal, are quite trainable with time, patience, and skill. Their distasteful origin is typically not brought up.
Trolls: Trolls are sentient bloodlines founded by two or more furies via sexual reproduction. Most troll bloodlines are humanoid, at least seven feet tall, and posses some form of natural weaponry and armor. Physically, most trolls are a match for the fury ancestors, and some can come close in magical talent as well. Trolls are unique among the dark races in that many of them eat to power their reproductive systems, healing factors, and growth.
Most troll tribes keep to themselves, and only take out their dark urges on their kin and their prey. Some trolls align loosely with the Drugar or Orcs; Although they are too violent and savage for a civilized race to allow them into the city in any great numbers, the strength, ferocity, and survival knowledge of the trolls make them valuable soldiers and laborers in rural areas.
Nightmares: Before the dark field of Durkim came about, those who practiced death magic could create transmittable states of undeath, and those who practiced life magic could make werebeings. Collectively these beings are called night creatures. The dark field can create similar creatures, called Nightmares, either through ritual or exposure to the bodily fluids of particular furies. It is usually possible, however, to determine whether or not a night creature is under the influence of the field.
All nightmares, like other creatures attuned to the dark field, are vulnerable to Bilestone, whereas night creature undead a revulnerable to various species of wood and night creature werebeings to various alloys of silver and/or platinum. Night Creatures must hunt to survive, while nightmares hunt to transmit their condition or to torment others. The transformation night creature werebeings is typically controlled by the winds, moon, and/or stars, while the transformation of nightmare werebeings is governed by their origins. Night creature undead are weakened or controlled inside of dwellings, and night creature werebeings can be weakened or controled via castration; Nightmares have no such weaknesses. Lastly a nightmare can be both werebeing and undead, which a night creature cannot be.