Neph'Kin

Ypogeios

There is an ancient network of tunnels and strongholds running under the mountain range of Fang. All of which connected to the myriad of cities that flourished here centuries ago. It is believed they served as places of refuge during times of great turmoil and war against neighbouring realms in the history of the mountain folks.
Now largely abandoned and shunned by the clansmen who believe the Ypogeios to be cursed. Or more accurately, diseased.

It is now home to a group of beings that call themselves the Neph'kin. They were once scorpion hunters, raiders, devil-worshippers and eaters of unleavened bread, from across the Great Desert of Skulls. Escaped when their brethren were taken as slaves, wandered the desert for far too long, fled below out of sun-madness and desperation to the caves and mines of Fang. Still fear thirst above all else.

Their coming and the decline of the civilization that once prospered in Fang, slowly but surely drove the clansmen above ground forcing them to leave behind their once mighty strongholds and underground cities.

Cloaked in symbiotic mould, that is extremely poisonous, except
to the Neph'Kin, causing blinding headaches and auditory hallucinations. Combat and fast movement shakes off the spores. They will stalk their prey in the dark for leagues, gently infecting brains, making one doubt its own sanity, turning friend to foe...

A deadly plague that pocks the skin and shrivels the mind keeps their numbers down, and often they capture interlopers to their domains to breed with, in an attempt to increase their dwindling numbers.

The Neph'Kin are the only people who can reliably make their way across thousands of miles of cavern without having to memorize every single twist and turn. Their language doesn't even have words for left and right - they don't need them. It's part of their culture, to hold the maps of the underworld in their minds...