Merwolf

When Malcolm is in the water he is transformed into the Lord of the Sea (a part-time job), and he must save his Dominion from the evil sea-wizard Nptananan who takes on many forms, his favorite being that of a merwolf with fangs like a viper.

Source: wiktionary

The Humdrum had turned the merwolves against the school, and they were crawling around, dragging their fins, getting everything wet and gnashing their teeth at little kids, and then Penelope Bunce, the hero of our story, cast a spell that made the clouds rain silver—

Source: wiktionary

Merwolf: On full moons, this creature transforms into a vicious wolf with the lower body of a fish. On other nights it is just a regular wolf, furiously dog-paddling in the ocean.

Source: wiktionary

A short drive down to a resort on the south coast and a chat with a woman who has had a Merwolf encounter. That'll be a new one for me. Merwolves... Amphibians, obviously. I’ve heard they have razor sharp teeth.

Source: wiktionary