In Philippine mythology, a siyokoy (syokoy) is an aquatic humanoid creature with scales, webbed limbs, and fins. Most folklore accounts describe the siyokoy as being hostile to humans, and are often associated with drownings.

This article relies largely or entirely on a single source. (April 2016)

While the siyokoy is often compared to the Western mermaid due to the Philippines' colonial history, its etymology suggests that it is actually of Chinese origin, which is highly plausible given that China-Philippines relations go as far back as 982 AD ^[1][2][3]),^[2] predating Western colonization of both countries.

The term siyokoy came from the Hokkien shui gui.^[4] In Chinese folklore, shui gui are the spirits drowned people who drag unsuspecting victims underwater and drown them to take possession of their bodies.

Compared to Sirena, Sireno, and Kataw who have human features, Siyokoys are of animalic in physical form and structure.^[5] Some people describe Siyokoy as...

...horrifying sea creatures with fish-like bodies and long green tentacles. They drown mortals and eat them. They have gill slits, are colored brown or green, and have scaly skin, comparable to that of fishes.^{[citation needed]}

Intimidating aquatic animals such as eels, octopus, rays and squids usually swim along with Siyokoy.^[5]