There are various magical spells, and potions that can accomplish this. You would need to contact a professional witch, warlock, wizard, or sorcerer to look into your options. In addition those who fall in love with a mermaid or merman can temporarily transform when entering the sea above the mystical confines of an undersea Mermaid community such as Atlantis. Lastly there is a method some can do on their own. If you happen to be a descendant of the lost continent of Atlantis you can activate your latent mermaid genes by drinking a potion made of Atlantic sea water, Atlantic Dolphin milk, Atlantic Seahorse oil, Sea Grape Juice ( Caulerpa lentillifera ), Irish Moss ( Chondrus crispus ), Red Seaweed (Palmaria palmata), and, marine eelgrass (Zostera). The potion must fill a large conch shell, be mixed completely, and be drunk directly from the shell. The shell must be from the Atlantic ocean or an Atlantic sea side beach. In addition the mermaid potion must be drunk while immersed in the ocean at least up to your neck under the light of a full moon. The Atlantic Ocean seems to bear better results. Within an hour you should transform into a mermaid or merman. If nothing happens within two hours then you have no Atlantean heritage in your genetics.