Mermaid colours for a different Halloween outfit, so fashionable and cute. You want a cool touch? Wear mirrored sunglasses: http://www.smartbuyglasses.co.uk/designer-sunglasses/Spektre/Spektre-Metallo-Rotondo-Silver-(Blue-Mirror)-292342.html
DIY mermaid hair extensions. fishing line, iridescent "bubbles" (large-flat-sequins, vary sizes) varying size pearl beads, maybe a few gold or silver filler beads, hot glue, star fish, hair clip. String accessories on fishing line, tie and knot onto clip, dab of hot glue for extra hold, hot glue star fish onto clip covering string, clip in!