Galatea

A mermaid in a well that showed up in Rosetta's backyard one day. For some reason, she really wants Rosetta to become friends with her. Galatea as a mermaid isn't actually real. The mermaid is actually a vessel Pygmalion made to try and lure Rosetta to being consumed by him, as he had done with the actual Galatea. Her last name is Andilet.