Isaac

Darkness Issac is a the leader of Mermaid and the second on command of Gabriella. Even though Don Salieri is technically the leader of Gabriella, Issac is the one in charge and is the one who commands the respect of the seven heads of Gabriella and the respect of the Mermaids. They see him as there real leader and only follow Don Salieri because of Issac's loyalty to him.