The first sign is the smell. Yeast and something sweeter beneath it - overripe grain left in a warm room, or the lip of a fermenting barrel on a hot afternoon. Then the sound: a low, wet gurgling, rhythmic and faintly obscene, coming from somewhere in the dark ahead. By the time torchlight catches the hump - swollen and amber-tinted, rocking slightly as the creature shuffles forward - the hopgoblin has already decided you are not worth running from.
The Shape of It
Hopgoblins are small. Rarely taller than 1.3 meters, they carry the lean, knuckled build of their goblin kin: wide shoulders for their size, long fingers, a hunched-forward posture born of carrying something heavy. What sets them apart is the sac. It grows from between the shoulder blades, a membranous dome that swells and shifts in color with whatever ferments inside - warm amber for mead, bruise-purple for wine, a clouded dark brown when something stronger is working. Their skin takes on a faint echo of the same hue. A hopgoblin mid-brew is never subtle. Their eyes tend toward the glassy and unfocused - not from lack of wit, but because they are, without exception, mildly drunk. The fermentation does not pause.
What Brews Beneath
The sac is the defining organ. A network of fermentation chambers runs through the hopgoblin's upper torso, drawing sugars and starches from whatever the creature has consumed and converting them, slowly and continuously, into alcohol. The liquid collects in the external sac, which can swell to larger than the creature's own torso before the pressure builds past tolerance. In the wild, venting is involuntary - a pressurized expulsion from the mouth that coats a generous radius in warm fermented liquid.
The brew changes with diet. Underground fungi produce a clean, malty mead. Deep grain stores ferment into something close to ale. Deepberry clusters - found only in the lower tunnel networks - yield a dark spirit that turns the sac nearly black and shifts the creature's temperament in ways the Duergar have learned to respect.
Temperament
Timid is the word most reach for, and it holds - mostly. A hopgoblin encountering something unfamiliar freezes, turns its body sideways to protect the sac, and watches. Given time, it moves on. Given food, it leans in.
The gift exchange is not a trained behavior. It emerged. Hopgoblins that were crowded, grabbed, or had their sacs forcibly tapped responded with the wild vent - a face full of pressurized mead at close range. Hopgoblins that were offered something first remembered it. Over generations of contact with Duergar, that memory calcified into expectation: an open hand with a small offering, held flat, means the transaction is honest. Push the terms, and the creature will enforce its own.
Caverns and Surface
Hopgoblins are native to the deep tunnel networks beneath the Bifrost Isles, where warmth seeps from below and moisture keeps the fungal growth thick. They surface occasionally, drawn by smell toward grain stores, refuse heaps, or the ambient yeast of a working brewery. Most surface encounters are brief. A few have learned that tavern districts are reliable foraging grounds and return with enough regularity that some establishments have started leaving offerings out.
Among the Duergar
In Nidavellir, hopgoblins are a fixture. They move through the lower market streets in loose clusters - unhurried, slightly swaying - pausing when someone makes the offering gesture. Duergar children learn early how to read the sac color and what it predicts about the creature's mood. A black sac gets a wide berth. A golden one gets a cup.
A handful of Duergar families have built operations around it: corrals of hopgoblins fed specific diets to produce consistent brews, the output tapped at intervals and bottled under house names. The finest stock is kept for generations, the diet-lineage guarded like any other trade secret. The hopgoblins, for their part, seem unbothered by the arrangement. They have warmth, food, and no predators.
Whether they understand the rest of it is unclear.
A creature that learned to barter before it had a name for the act. The Duergar, who respect very little, have found in the hopgoblin something almost like a peer: something that knows when it is being cheated.