Planet Lore: A World on fire, seas of molten rock flow across a land of blackened rock and the few instances of water on the surface are a boiling brine that would be too toxic to drink if it didn't melt the skin off your body. Far below the dangers of the surface a network of caverns connect in a vast honeycomb of the only real life on the planet as fungus grows from the heat and springs of fresh water and blind creatures feed off the fungus only to be fed on by the Duergar or the few species of dragon too small and flightless to survive on the surface. Three kinds of beings dominate this molten world: The Duergar deep below the surface who make up for their physical weakness through powerful industry and runecraft, The Earth Spirite who travel between the astral plane and ours who claim territory within the oceans of lava and are unpredictable either trading of the lands bounty in return for tasks or destroying oncomers on sight, and the Great Dragons of the surface world who are only interested in dominance fighting great battles across the sky for dominion or enslaving any race on the surface to provide wealth and tribute. The balance of the world is enforced by the hostile conditions as a Dragon can't travel to the realm of the Duergar and will be dragged to its death should it try to fight the Elementals in their territory and the Elementals can't protect themselves outside of their home of liquid rock and the Duergar can't fight in the sky or molten rock.
The planet itself is just as deadly as any foe as the Ash filled skies choke away at all but the elementals and the pools of lava offer no safe haven for life to thrive. Even below the world is just as much a threat as it's denizens as the vast caverns are more likely to be filled with toxic gas than life sustaining water and any life that manages to survive has the true viciousness of something desperate to survive.
Background: Former slaves of the Dragons that to this day rule the molten surface world, the Duergar escaped millenia ago and have lived beneath the surface ever since refining the runic magics that power everything from their tools to the cities themselves. Despite their hard past this is still a world of dominance and as such the Duergar keep slaves just like the dragons except theirs are earth elementals they managed to trap in bodies of obsidian and steel under the guise of false promises and the powers of binding runes. The same has been attempted on newborn dragons but as the beasts grew in age and power they eventually broke free and usually destroyed their former masters. The society of the Duergar itself is a strict class hierarchy with the Runesmiths of House Durn at the top, their retainers below them, and their retainers below them and so on and so forth with the slaves.
The Duergar have gone to war with the dragons many times in attempts to reverse their past and each time are sent back below the earth and even now they gather their artifacts and work to gather more enslaved elementals to become the rulers of the surface as well as the underground.
A major influence on the Duergar is their world's close proximity to hell which has allowed a slew of infernal forces to influence the species itself and forever marking the species as diabolic in nature and the same can likely be said for all species of the world for even a few drops of demon blood run deep.