Night Goblyns

The Night Goblyns were started by a goblyn Khadine named Rashmish who led her tribe underground to escape the ruin at the end of the war with the gods. Rashmish was a True Goblyn, which means that she was alive before war began and survived through it from beginning to end (her soul was intact and undamaged by Baulk). She was one of the first Khadines, meaning she was tested by Skribbit himself, when he was still a mortal goblyn. During the war she made her way to the Elven afterlife and stole the eyes from their weaver of fate, leaving it blind and granting her foresight. When Rashmish returned from the other world, she had visions of Neb being killed by elemental beasts, of Sifu being cursed and changed, of Skribbit, burning in rage and streaking across the sky, and of Reth, chained and condemned before the other gods. She rushed to the goblyn stronghold to find that these were not just visions of the future, and that the first three had already come to pass. She finds Reth, who is preparing for the final attack on the gods. Reth realizes what is going on with Rashmish's visions and forbids her from telling him his own fate, but instead tells her to use her visions of the future and do what she thinks is best for the survival of the goblyns. Filled with bitterness, she watches the great goblyn army march away to their doom, before leading her own tribe down deep below the mountains, to survive and grow strong.

So according to this origin, the Night Goblyns descend from Rashmish and her tribe. It makes sense that other goblyns would have fled beneath the mountains over the years and joined the Night Goblyns. Night Goblyns are not a different species from normal goblyns, but have a different culture. They wear hoods when above ground because they hate the sun and it is painful to their eyes, since they live their lives underground. They have a love of psychedelic mushrooms. Over the years if they eat too many of these mushrooms (and who wouldn’t) they can become dangerously insane or unstable. They wear the checks and dags (triangles) because they eat so many mushrooms, that the lines of everything begin to blur. So checks and dags are so that you can tell where the edges of the goblyn are, and that they are therefore real. They are still Goblyns, but with a different history from surface goblyns in that they never grew weak or cowardly.