Winx Club: Season 0, Episode 8

0 - 8:

Taking place before the sixth season, the Trix try to activate the Emperor's Throne and inadvertently free Politea. They kidnap Sky to free Tritannus from Oblivion and acquire a magical pearl that will allow them to obtain the power of the Emperor's Throne. The Winx will have to go on a Sirenix mission in the Infinite Ocean to stop them and save Sky.