Giant Damselfish

The giant damselfish is a slender, dun-brown fish with a heavy, bony skull. Its real secret is a modified dorsal fin that unfurls into a long streamer shaped roughly like a human woman. Folded down, the fin is just a ridge along its back that helps it swim.

At night the fish drifts at the surface, head down and tail slack, with its lure raised. When it hears a boat or someone walking the shore, it twitches and flutters the streamer so that it looks exactly like a human or elf woman struggling to stay afloat. If anyone grows suspicious, the DM secretly rolls an Intelligence check on 1d20 for each character; a failure means the illusion holds.

When a rescuer comes within 10-15', the 'lady' gives a final thrashing plunge and vanishes. The fish snaps its fin flat and drives its skull into the swimmer for 1-4 hp damage. A successful ram lets it make an immediate second attack at +2 to bite for another 1-4 hp; a missed ram means no bite that round. Afterward it circles and rams whenever it gets an opening.

A natural 20 on the ram stuns the victim for 1-3 rounds. During that time the fish lands its ram and bite automatically twice per round, for 4-16 hp each round, and cannot stun again until the target recovers.

These fish favor warm, shallow seas. Each one claims a square mile of water beside a shipping lane and holds it until passing traffic dries up. Males and females meet only to mate. The female carries the eggs inside her until they hatch, then bears as many as 25 young, which race away before their mother can eat them.

The taste for human and demihuman flesh, along with the full damsel fin and the instinct to fish with it, arrives only with adulthood. Some sages think an archmage or a greater power bred the species. Adults are savage enough to attack anything nearby, which feeds them well on other fish and gets them killed when the neighbor is a shark.

Damselfish keep no treasure, though a gutted specimen sometimes yields a swallowed valuable. Their flesh is far too tough and pungent to eat. The only real demand is for the dorsal streamers, which can replace the fleece in a phantasmal force spell or any other illusion/phantasm spell that calls for it.