Here's a fun project!

You'll need:
BIG paper (36 inch wide butcher paper works well)
Pencil & felt pen markers
Tissue paper, shiny paper, foil, or favorite paper scraps
A glue stick or white glue
Optional: Glitter jewels, fabric, shiny candy wrappers, fancy papers, & watercolor paints

Here's what to do: Lie down on a large piece of butcher paper and have a friend or grown-up trace around your outline in pencil. Keep your legs together (mer-creatures don't have legs, you know). When you get to your knees, draw a tail-fin shape instead of feet. (Teachers, if you are doing this as a class project, you might want to cut out a few cardboard tail-fin templates in advance for quick and easy tracing).
Next, outline your shape with felt pens, and draw the details of head and hair. Draw in a wasitline & belly button.

Mer-girls, decide whether you want a swim suit top, sea shells, or seaweed floating by up top--whatever it is--draw that in.
Then use torn tissue paper, or your favorite shiny candy wrappers, the funny pages, or scrap paper to glue a colorful design on the tail-fin.
If you have glitter jewels, or other decorations, glue them on as desired.
Some kids like to draw in or glue on a glittery crown, jewelry, hand bag, shell-phone, and other fancy stuff.
If you still have time, draw or paint in some seaweed, fish, sand, waves or other background.