Part octopus, part glider, part stalactite, the darkmantle is a common subterranean hazard.
Pilgrims are disappearing from the Grotto of the Saint. The few victims who have escaped the strange assault cannot describe their attacker—custom dictates that supplicants enter blindfolded. The few guards that have been sent to search report falling victim to darkness, as if the Saint was insulted by their unbound eyes.
A seaside cliff is riddled with caves known collectively as the Vaults of the Agathions. The acoustics within are said to echo secrets whispered from the Upper Planes. An aquatic species of darkmantle makes visiting the Vaults a dangerous prospect, however.
An apprentice wizard is sent to retrieve darkmantle organs for his mistress’s experiments with magical darkness. She demands he bring a caged goblin to use as bait—an arrangement neither of the pair is comfortable with.
—Pathfinder Bestiary 55