Amy the Siren was the disguise of Amy Cavenaugh. She tipped off Velma Dinkley about the missing sardine boat and met Velma in the guise of a singing mermaid, in order to get Mystery Inc. to investigate the disappearance of her husband, Dr. Spike Cavenaugh.
She is a siren/mermaid hybrid; she looks more amphibious than human.
She used what she had learnt about Velma and tried to befriend her and get her help.
Powers and abilities
She has a haunting singing voice. Her swimming ability is excellent, so that she can leap great distances out of the water.
Scooby-Doo! Mystery Incorporated