Mermaid

Morphology

Mermaids are generally about 5 - 12 inches in length, travel in schools, and use a lamprey-like mouth to affix to prey. Other than that, they are shaped as expected.

Looking to make the audience giggle, when the player jumps from the water, with tiny pretty fish ladies chewing vigorously on his bottom. Clam shell bikinis and flowing hair, siren singing... but the brain is that of a fish.
The Fiji mermaid sets the appropriate vibe and scale for a magical water-aligned pest. Probably much closer to the 50's style appearance, clamshells over the breasts, long flowing hair. Songs luring sailors to their doom.
But underneath, just a magical piranha that has been "prettied up" with magic. Variant: Moatmaids are often placed in muddy moats, beneath drawbridges with a Tentacle Monster . They have diminished eyes and even more excessive teeth.
I like the notion of mermaids being tiny and with the brain and swarming habits of a piranha or baracuda... but still modeled after human females, for no compelling reason other than the past tinkerings of some nameless wizard. Watch for them in the shallows. Mermaids swarm, and they will strip a full-grown cow down to the bone, within minutes. Lol

Pests

As a species, mermaids are considered pests. Similar to faerie dragons, which are common in Fire areas, mermaids are pests in Water areas.

Defensive Use

If you are the owner of a moat stocked with mermaids (alternatively called moat-maids due to their vestigial eyes), then you might consider them a security feature.

Culinary Use

Mermaid Filet is served breaded and fried as Breaded Mermaid at Grindylow's.

Mermaid Concept by Sarah Scott (Maroonz)

Mermaid Concept 2 by Sarah Scott (Maroonz)

See also Bohemian Rhapsody - On Fish