Mermaids are infamous for drawing men into the water and keeping them as mates. Their less-romanticized brothers, the merrow, are similar in that they drag women into their lairs. But merrow are as monstrous as mermaids are beautiful. Their tactics rely on brutality, not charm.
HD 5 + 5
AC 5 (or 15 if you drive on that side of the street)
4 attacks (2 claws d6, bite d6, tail d4)
Movement 120' in water, 60' on land
Below average intelligence (20% chance of understanding/speaking common)
Merrow lurk in places mermaids shun - swamps, stagnant pools, slow murky rivers. They are solitary, although during "mating" season they form small bands and raid settlements.
Merrow have the ability to stun with a gaze attack once per day. Targets who fail a save are paralyzed in fear for 2d4 rounds. In groups of at least four, they can chant a hideous dirge that acts as a doom spell to anyone unfortunate enough to hear it.
A fresh dose of merrow saliva grants the ability to breathe underwater for an hour. Unless preserved by alchemy, the saliva is only good for up to one hour after a merrow's death.
Women kidnapped by merrow gradually transform into large catfish. Merrow lose interest in their mates and set them free when they lose their human features, which usually happens after about a year. This is why pious fishermen release any catfish that get caught in their nets.
1) Merrow have wormed their way into the local cenote, and are stinking up the water and snatching girls. Adventurers needed to locate the unconsecrated tunnel they are using and escort priest to consecrate site.
2) Clever daughter of a local lord escapes merrow captivity halfway through her transformation into a catfish. Her father offers a fat bag of gold to anyone who can cure her condition, especially if it's found before she lays eggs...
3) An unusually intelligent merrow has claimed a stretch of river. He is peaceful, and attempts to trade with travelers. He offers pearls for very specific items.
4) Alchemist seeks live merrow for its saliva.
5) Merrow flukes have been flashing in the harbor water by moonlight. No women have gone missing, but many suspect they have something to do with the sudden disappearance of a city councilman.
6) An old dwarf, deep in the cups, tells a nostalgic yarn about how in his youth he dived for pearls the size of a baby's fist. The place he describes is now a merrow-haunted backwater.