Tritannus is the main antagonist in Season 5. He was once a normal triton, the son of King Neptune and Queen Ligea , and the twin brother of Prince Nereus who was jealous that his brother had been chosen as future King of Andros instead of him. He tried to disrupt his brother's crowning ceremony, but was arrested and sent to prison. He later escaped to Earth and was turned into a monster by pollution and allied himself with the Trix. His goal is now to rule all the world and to conquer the Infinite Ocean and caused pollution so that he may grow stronger. The Winx go underwater to fight him, but their Believix powers are not enough. They will have to look for the Sirenix power and become mermaid fairies.