Based on a dream I had, I designed a creature that is “the natural predator of merfolk” (I call her a Xocduct, which roughly translates to ‘seductive ancient shark’)
A massive sea witch with a humanoid ‘lure’ on the top of her prehistoric shark body.
She is a rare sea monster that can enchant merfolk and pick them off one by one. Mer-people are naive and naturally trusting of other aquatic humanoids, and this paired with the Xoducts inviting nature, causes whole villages of mer-people to vanish without a single sign of struggle.This one is a juvenile Xocduct named Ecrive. She wanders a little too close to the shore and gets trapped between some reefs and the shore.
Luckily she is able to get in contact with a Marine Biologist named Teja who wants to help this mysterious primordial creature despite the danger.
Don’t fall for a Xocducts charms, it will feed you honey lies and sing deeply haunting songs too low for Merfolk to sign in their soft upper registers. Almost everything about them is to snar prey, even the humanoid torso is just a lure they can live without.
And whatever you do don’t kiss the giant enchanting sea witch, they can transform humans into merfolk and they don’t show merfolk the same respect they show humans.
“The natural predator of merfolk”
I like this very much so.