The Night Goblins are a subspecies of Goblin found in the Warhammer Fantasy universe. Their prime biological distinction from other Goblins is their extreme sensitivity to light; they live only in the deepest caves, and only emerge from them upon the darkest of nights. Their iconic black robes serve to shield as much as their skin as possible from light and to allow them to easily blend-in with the pitch darkness. Their subterranean nature makes them the natural enemies of the other underground races, the Skaven and Dwarfs.
Night Goblin agriculture is primarily based around Squigs and mushrooms. Squigs provide meat and attack animals, while mushrooms are used as both food and psychedelics, be it to provide their shamans with mystical visions or drive their Fanatics into a battle frenzy.
The most famous Night Goblin to ever live is Skarsnik, the warlord of Karak Eight-Peaks.
In Age of Sigmar
The Night Goblins in the Mortal Realms have been renamed the Moonclan Grots. The most important distinction between the Night Goblins and the Moonclan is the Moonclan's worship of the Bad Moon. This rogue celestial body is believed to hold Gorkamorka's power, and spreads madness and fungi wherever it goes. The presence of the Bad Moon fills Grots with an energy akin to the Waaagh! known as the Gloomspite (differing in that it is fueled by spite and treachery instead of primal aggression), resulting in them coming out of their underground lairs to overwhelm the surface. The dream of the Moonclan Grots is to somehow impress the Bad Moon enough that it chooses to stay in one place indefinitely, ushering in an age of darkness referred to as the Everdank. The closest anybody has ever got is Skragrott the Loonking, whose conquest of the land of Adayah managed to impress the Bad Moon not into staying, but into spitting out a cloud of debris to blot out the sun and allow him to keep an above-ground empire.