Source: Monster Codex, pg(s). 232
Sewer trolls are lankier and smaller than common trolls, only weighing around 200 pounds and reaching up to six feet tall. Their eyes absorb ambient light, which temporarily blinds them by damaging the slimy membrane that covers them. As the membrane regenerates, a reaction causes the eyes to glow orange. Sewer trolls are very flexible and have oversized claws.
Sewer trolls regenerate all damage not inflicted through fire or acid, though more slowly than normal trolls can, and they need a lot of food to power this ability. Due to their flexible bodies, they can ambush prey from small spaces that appear incapable of housing a threat. They eat almost anything, but prefer fresh meat, preferably that of endothermic over ectothermic creatures.
Sewer trolls live underground, in areas with sufficient food: the name 'sewer troll' originated from their lairs in the sewers under cities. Each major city is usually home to dozens of sewer trolls, who ambush children just below sewer grates. These trolls rarely go to the surface due to their light blindness, except in desperate times and only at night. They stick to the shadows and ambush lone pedestrians, or sneak through windows to snatch babies, but are easily scared on the surface.
Sewer trolls sometimes join groups of common trolls or scrags to benefit from protection. Because of their smaller size, they are often bullied and forced to do menial chores or be the first to enter unexplored caves, but many sewer trolls accept this as inevitable.