Mermaid costume ideas?

I'm going to this costume ball and I'm using my old prom dress because it looks "mermaidy". I need some ideas of stuff to add to the costume. For my hair I think I'm gonna wave it so it looks like it dried wet and maybe put some random braids in it. Also I was going to put some shimmer lotion on or something. What are some suggestions for jewelry or some kind of ornament to put in my hair or other suggestions?