Winx: Mystery of the Abyss

The Trix witches are in the Infinite Ocean, unsuccessfully trying to harness the power of the Emperor's Throne. They end up accidentally summoning the cursed nymph Politea and engage in a battle with her. Politea informs them that the throne will only empower the true emperor, Tritannus. The witches make a deal with Politea to return Tritannus from his prison in the Realm of Oblivion, which is only possible with the vital force of a young prince. Once they free Tritannus, the Trix plan to convince him to retrieve the mystical Pearl of the Deep, which will free Politea from her curse so she can help the Trix.