I assume you use a 3D program for her, it’s better if you post the wireframe as well so people have a better look how things stick together. Maybe other people can help you with how to model tentacles, never done it myself.
There’s no background yet, so it’s hard to give a bit more atmosphere. Usually people use misty/dark backgrounds with visible light for a bit of mysterious atmosphere. Ow well you know your movie/videogames classics i guess
She has no features that make her look dangerous, you could give her claws or other physical features or maybe there’s something special with her face.
But it’s a bit rough as it is now, why don’t you make some scribbles for the mermaid/background and work on her tentacles so there’s more to comment on, this way it’s not clear where you want to go, since there are no scribbles/concept/background just this model
Don’t forget you need to know what you want or you can’t ask for specific help