Death Minnow

Bright orange and just 2 inches long, the death minnow is a magical guardian of undersea lairs and hoards, bred from ordinary deep-sea fish by unknown makers (aboleth, sahuagin and sea elves are all suspects). It finds prey with its lateral lines.

Its makers gave it an innate power equal to enlarge/reduce. It approaches any target no bigger than size M, then swells in an instant to the bulk of a giant angler fish, inhales its target and shrinks the two of them back down to minuscule size. Unless someone was looking right at the victim, the person seems to vanish into thin air.

The suction gulp itself does no harm, but stomach acid deals 1d6 hp damage each round until the prisoner dies or is freed. The fish is magically compelled never to release a meal, so it must be killed, at which point the victim returns at once to full size. Even swollen with prey it dodges most blows easily, and weapon strikes harm the swallowed victim as much as the fish. A quick-thinking wizard can cast dispel magic on it, restoring it to its true 8-foot form and making it far easier to hit.

There are no wild populations; being magical creations, they need not breed and may not even have sexes.

Its only ecological effect is keeping its post empty of other life. Its blood is useful in ink for scrolls of enlarge or reduce. Anyone wishing to turn the tables and eat the fish will find it tastes a lot like kippered herring.