Rays that fly. Cloaks that come alive. Geniuses too mad to cooperate. Worshippers of gods too alien to answer back. Ties to aboleths, vampires, and the Plane of Shadow. Whatever else you may know of cloakers—Sean K Reynolds gives an excellent rundown in Dungeon Denizens Revisited—the central takeaway should be one of wrongness. All aberrations should feel just that—aberrant—but a good cloaker encounter should leave PCs and players alike shaking their heads and shuddering.
Worship of Cerneres, god of secrets, confessions, and knives, has been officially discouraged for some time. Yet when priests of Cerneres rededicated the temple in Whitegate, they did so unmolested. Anyone approaching the priests in their black leathery cloaks fell ill or succumbed to panic. Now Whitegaters leave the priests be and turn a blind eye, though beggars tell of strange shapes fluttering into and out of the temple after dark.
An ancient skum archivist and a nascent cloaker lord have reached a strange détente. The cloaker demands obeisance but craves knowledge of the ancient aboleths, whom the archivist served firsthand. The skum is no match for the cloaker’s power, but doles out his secrets slowly in exchange for captured humanoid wives.
A starship shaped like a manta ray sails through the void of space. Boarders will likely take the ship to be unoccupied, as there is no sign of humanoid life and only a rudimentary helm. However, a strange aviary on the poop deck is actually the bridge. The cloakers inside slumber, but if aroused their strange flight patterns actually steer the ship in a blend of wing beats and prophecy.
—Dungeon Denizens Revisited 10–15 & Pathfinder Bestiary 47