In the mermay spirit, here is Yue

I eye dropper picked the colours from images of pre-moon-spirit Yue and of the original moon spirit fish (RIP)

Basically I gave her moon spirit form the tail of the first moon spirit, since if she was a mermaid that is definitely the kind of fish she would combine with

I was originally going to do Katara after seeing an image of her as I was scrolling but then I realized doing Yue would be a much better option due to her actual ties with a fish