User blog comment:RoyallyBella/Mystery of the Abyss expectations blog/@comment-4954276-20140531140744

For everyone wondering, the Trix capture Sky in the third movie because Politea told them there is still one way to be able to active the Emperor's Throne: to take a king's vital force. After they free Tritannus and convince him to ally with them again to take the Pearl of the Abyss. In the movie, it is both Sky's life and the balance of the Infinite Ocean the Winx are fighting for. And for Politea, she's still in her nyphm form, but unlike Daphne, she is still under the curse of Sirenix. All this can be found on the third movie page. So no, for those who thought that, Politea is not a Selkie. She is still a nymph cursed by Sirenix. And the Trix want to kill Sky by taking his vital force to activate the Emperor's Throne. That's why he is in the Infinite Ocean.