Mermaid Costumes Dizguise.com has Mermaid Costumes for both children and adults. Mermaids are legendary creatures of the sea found in movies such as Little Mermaid, as well as in numerous books and fairy tales. Little Girls love to dress up as a mermaid, and big girls like to go to parties as a mermaid. So whether you are having a Mermaid Costume party, going to another special costume event, or just wanting to have fun dressing up as a mermaid, a mermaid costume is a great choice for your fun time.