They look like miniature mermaids with transparent flaps of skin under their arms which allow them to fly, but have no real wings.They are usually purplish or bluish in color, except Lusiz, who is pale green, and the Queen of the Undines, who has golden skin.
They appear to the Winx throughout Season 1, but do not make appearances in the other seasons. Their main role occurs in Episode 11 of Season 1, where the Winx accidentally meet them ,after Flora had to move to the Black Mud Swamp ,after her experiments were troubling the other Winx girls at Alfea .The Queen of the Undines, Algae, told them that they live in a miniature underwater town of bubbles, found in the Swamp which they make using a plant called Zilith. She then explained to the Winx that obtaining the Zilith was very dangerous for them because there was a gigantic monster in the Swamp which terrorized them and that an Undine sometimes volunteers to go to the island and pick Zilith leaves but that the last one who went, Lusiz, never came back.
The Winx then decided to fight the monster and look for Lusiz but were attacked by the monster, which captured Musa and took her underwater. After saving Musa the Winx landed on the island and found many Red Willow trees growing in a spiral shape around their leader tree.
The Winx nearly all fell asleep except Tecna who analyzed the air on the island and found out that it was a kind of sleeping gas. She then woke Bloom up by making a bubble of clean air around them and they made the bubble bigger and awoke the other Winx girls. The Winx girls together made the bubble even bigger and wake up Lusiz, whom they found sleeping at the base of the Leader Willow.
Lusiz explained them that what they thought was a monster, was in fact an enormous turtle whose shell was the island on which they were and which was sleeping because of the sleeping gas given off by the Red Willow growing in it. She told them that the turtle was a sleepwalker and that when it moved its head in and out of its shell while sleeping it would look like a monster and scare the nymphs away. The Leader of the Red Willows tried attacking the Winx but was defeated by Flora and Bloom and freed the turtle who woke up.
The turtle then moved away after allowing the Undines to pick as many Zilith leaves as they could from its back but the Undines only had a limited supply of Zilith leaves which would end up by running out and the Undines would have to live exposed to predators after their stocks would end up. Flora then decided to use a rapid growth formula she invented to make new Zilith plants grow for the Undines so that they could safely in the same place forever, and the Undines gave her a Cheerful Gladiolus, the flower she had been looking for, as a way of expressing their gratitude towards her.
The Undines appear again in The Ultimate Challenge. From the shores of the Swamp, found near the road from Cloud Tower to Alfea they see the Trix leading the full force of the Army of Darkness for their final assault on Alfea. They fly to Alfea where they warn Faragonda of the danger.
The last appearance of the Undines is at the end of the last Season 1 episode, during the party at Alfea. They fly above Alfea in the night sky, shining like fireflies in the dark and leaving a trail of sparks behind them.
- The Undines do not have wings, but instead have transparent flaps of skin under their arms which allow them to fly.
- They seem to have nature-based powers and to be very in touch with nature for the following reasons:
- Lusiz explained that while she was asleep under the Red Willow she was in telepathic contact with the environment around her.
- The Undines gave a Cheerful Gladiolus to Flora which they told her would allow itself to be picked only by her while Flora had earlier mentioned to the Winx that the Cheerful Gladiolus cannot be picked because it has thorns. This means that the Undines were able to get in touch with the Cheerful Gladiolus to convince it to allow itself to be picked by Flora. The Undines probably need to have nature-based powers to be able to contact the Cheerful Gladiolus in this way.
- The Undines can shine in the dark like fireflies and leave a trail of sparks behind them.