Shimmerfish

Shimmerfish look like sleek, strong dolphins and leap in the same arching bounds, often riding a ship's bow wave. Young ones are dull-skinned; at about six years old they mature and their hides begin to shimmer and glow.

By arranging their luminous bodies underwater, shimmerfish form crude pictures, often golden treasure on the seabed or glowing humanoid figures. When four or more do this together it becomes a magical lure: anyone who sees it must save vs. spell or be entranced and leap in after the prize unless held back by force. Once the victim is swimming, the pod closes in and bites with hundreds of razor teeth. Lifelong sailors and fisherfolk get +4 on this save; green hands have the worst of it.

If the lure fails, they ram small boats at speed, one after another. Each ram forces a save vs. crushing blow or the hull springs a leak and sinks in 1d4+6 rounds. Leaping as high as 6 feet, a shimmerfish can also bowl people off the deck: if its attack roll hits, the target must save vs. paralyzation or be knocked into the sea.

They love dragging out terror. Some 'rescue' shipwreck survivors, carry them almost to shore, and then turn on them just to watch hope collapse.

Shimmerfish swim only in warm salt seas, never fresh water, trailing schools of fish in usually small groups that sometimes join briefly into larger ones. A cruising speed of 19 miles per hour is easy for them, sprint past 25, and can dive below 1,000 feet for short spells. Their language of clicks and whistles doubles as echolocation, like a bat's, for navigating and finding prey.

Each eats nearly a third of its body weight daily, mostly fish and squid. They mate in spring, carry young for eleven or twelve months, and the calves swim and breathe within minutes of birth.

A gland in the head holds about an ounce of fine oil prized for lubricating delicate mechanisms, worth 1 to 5 gold pieces. A raw hide fetches about 2 gp, and a cured one is lovely enough to be worth at least 10 gp.