Beast of the Depths

The Beast of the Depths is a monster the Trix commanded to attack the Winx Club and Daphne in the first episode of Season 6, "Inspiration of Sirenix". According to Daphne, the beast can never be destroyed/defeated/killed, but can be controlled by a powerful entity. This creature is also immune to the Dragon Flame.

Season 6
During the celebrations, The Trix command the Beast to attack Daphne. While Daphne is frozen with horror, the Winx and the Specialists attack the Beast with no prevail.

Later on in the episode, the Winx convince Daphne that she can transform into Sirenix and will be able to drive the Beast away. Daphne succeeds in transforming and commands the Beast to return to the depths of the ocean.