in true Halloween form i have put together a tutorial using some products recently sent for review. the product shown above is a limited edition JulieG nail polish for Jesse's Girl Cosmetics. Jesse's Girl is a great option for Halloween makeup if you are going for those great makeup looks (like the MAC ones i previewed here).
perhaps you were thinking along the lines of mermaid? check out my fish makeup tutorial here which would work perfectly with the nail tutorial below for scale nails:
#shoutout to the Limited Edition Cynthia Rowley Tweezerman