Copy and paste, blending layers. Add some ocean waves and bubbles brush.
Thanx to bugudifino http://bugidifino.deviantart.com/art/Mermaid-and-other-poses-15-245583926 and for the great tail to http://browse.deviantart.com/resources/?q=fish%20tail#/d2dvua8

This mermaid is only found in the desert dunes of the sahara and you can only see her when your extremely exhausted and very thirsty.

Use photoshop and illustrator to create this image. Many thanks to Avieth for the gorgeous lady model.

special thanks to:
Eastop (http://www.sxc.hu/profile/Eastop) for the starfishes i used on the mermaid's chest
and Pinkvelden (http://www.sxc.hu/profile/Pinkvelden) for the amazing photo of the floating market on the background :)