Omnia is the supreme guardian of Sirenix and invites the Winx and selkies to enter the infinite ocean after they complete the quest for Sirenix.
Politea is a Sirenix fairy and was Daphne's best friend. Politea and Daphne fought against the Ancestral Witches to protect the Magic Dimension but she betrayed Daphne to the Ancestral Witches and they placed a curse on Sirenix which turned Daphne into a bodiless spirit and Politea into a monster who lived in a cave in the Infinite Ocean. Darcy and Stormy stole Politea's Sirenix and she disappeared completely, though she merely could've materialized somewhere else. She's supposed to be a villain for Season 6.