Dark Sirens

The Dark Sirens are a group of evil mermaids who kidnap Andros' queen every time the Mermaid's Tail constellation shines brightest in the sky. Mysteriously tied to the constellation, the Dark Sirens seek to bring their group up to five, one siren for each star in the Mermaid's Tail, as it is said that they will become unstoppable once this comes to pass.

Members

 * Limes is the leader of the Sirens and the youngest. She has dark blue hair and demonstrates powers over darkness; specifically light absorption and darkness expansion.
 * Terala is the Siren with red hair who is seen shooting poisonous quills from her palms.
 * Unla is the Siren with orange hair who is seen shooting bits of coral from her palms.
 * Nazca is the Siren with seafoam-colored hair who is seen shooting blasts of darkness.
 * Asfodelia is the fifth and final Siren needed to complete the group. Had the ceremony gone uninterrupted, Niobe would have assumed her identity.

History
According to King Teredor, the Dark Sirens were once beautiful queens who faithfully served Andros in ancient times before they were forcibly turned into creatures of darkness. Approximately one thousand years ago, the last of Andros' queens, Queen Limes, was kidnapped by the Dark Sirens and turned into one.

#107: The Dark Sirens
At the very beginning of Issue 107, a warning sign signaling the titular Sirens' impending arrival is shown before their physical debut. The Winx catch sight of this warning sign: the five stars of the Mermaid's Tail suddenly changing in alignment. As it turned out, Aisha was called over to the Royal Astronomical Observatory by her father to further examine the moving stars. Realizing what they symbolize, Teredor and Aisha rush for the Royal Palace of Andros to warn Niobe but, when they arrive, Niobe is nowhere to be found and her bedroom had been completely trashed. At the foot of Niobe's bed laid a coral necklace, one that Teredor immediately recognizes it to be the custom signature of the Dark Sirens; something they leave behind at the scene of their attacks. Once the Winx and most of the palace guards have been called to the top of the Royal Palace, Teredor explains that the Mermaid's Tail constellation is one that only the Kings of Andros have been able to understand for generations. He then explains that creatures of darkness known as the Dark Sirens emerge from the darkest and deepest depths of Andros' oceans when the constellation shines at its brightest, and travel through all bodies of water to reach the mainland. Nazca, Terala, Unla and Limes are the names of the four Sirens and Teredor reveals that each one of them were once queens who ruled over Andros in ancient times. Queen Limes was the last of Andros' queens to be converted into a Siren and tonight, the Sirens plan to convert Queen Niobe. With all this information, Tecna deduces that the Sirens want to complete their group by bringing it up to five and Teredor tells the girls that the Sirens would become unstoppable if that were to come to pass. So, to rescue Aisha's mother and stop the Sirens, the Winx go into their Harmonix forms and dive into the murky waters of Andros. Upon entering the oceans, the Winx are attacked by Terala and Unla, who use the surrounding coral as camouflage to confuse the six fairies. The two then sneak up behind Stella and knock her unconscious. With the Winx diverting their attention to Stella's wellbeing, Terala and Unla flee into the Deep Blue: the heart of the Andros Abyss and the home of the Dark Sirens. In the Deep Blue, the four Sirens attempt to convert the captured Queen Niobe into becoming Asfodelia, the fifth and final Siren. As Niobe resists them, Limes tells Niobe that, regardless of her decision, she will be lowered into the darkest part of the Deep Blue, where she will be forcibly turned into a Dark Siren, assume the name Asfodelia, and completely forget her past as Niobe. The Sirens continue to taunt Queen Niobe until Aisha ambushes them with her Mystic Veil, hitting Unla and surprising the other Sirens. Acting quickly, the Sirens do battle with the Winx as the Selkies lead Niobe to the surface while everyone is distracted. Using her powers over darkness, Limes amplifies the darkness of the Deep Blue and strips Stella of her light when she tries to counteract Limes' darkness with her Shining Mirror spell. There, the four Sirens unleash a powerful Convergence on the Winx, leaving Musa and Tecna barely able to shield themselves and their friends. The Sirens' Convergence is quickly mitigated by Flora who uses the light of the algae to blind and weaken them, giving Aisha an opportunity to blow back the Sirens with her Thirteenth Seal.

As their defeat draws closer, Limes demands to know the identity of the powerful fairy who opposes them, to which Aisha proclaims herself to be the Princess of Andros that the Sirens made a grave mistake in challenging.

Amplifying her Thirteenth Seal, Aisha pushes the Sirens into the murky abyss of the Deep Blue, where the four former queens are immediately trapped inside an inescapable whirlpool that pulls them farther down.

With the Sirens properly disposed of and Niobe returned safe and sound, the Winx return to the surface to relay the good news to all the land-dwelling people of Andros.

Trivia

 * The fifth and final Siren, Asfodelia, is the only one of the Sirens who never makes an appearance. This is because Niobe was supposed to become Asfodelia upon being converted into a Dark Siren, but she was luckily rescued by her daughter, the Winx and Selkies before then.
 * While it is explicitly stated that Limes was the last of Andros' queens to be converted into a Dark Siren, it is unknown who amongst them was the first or how she was converted.
 * It is possible that the Dark Sirens are distantly related to Aisha's family since they were past queens of Andros.