Cave fisher
Cave fisher is a crab-like monster of the Underdark which hides on ledges and hunts by emitting a long strand of sticky filament to trap prey.
On the way to Blingdenstone, Jimjar recognized a strange filament ascending up to a ledge. He explained that it belongs to a cave fisher, hiding on top of the ledge overhanging the trail. Shortly thereafter a battle ensued in which it was clear that these creatures have highly volatile blood and were therefore quite susceptible to Bree's bonfires.