User blog:FabCassandra/Plot Summaries 8 - 13 *SPOILERS*

Episode 5X08: Tritannus raids King Neptune’s underwater palace and transforms his family into mutants. Then, thanks to the magic of his trident, manages to absorb the power of his father Neptune’s sword. The Winx are in Melody, busy searching for the second gem, the one of Empathy. During a fight with Tritannus, Musa is hit by a powerful spell and transforms into a terrible monster, bent on destroying the Winx. Daphne is captured by Tritannus and the evil Trix.

Episode 5X09 At Alfea College, Stella organizes a fashion show, but it’s not as successful as she hoped. While looking for ideas for new clothes, she is transformed into a three-year-old girl by an Age-Change item. In the depths of Zenith, the Winx, supported by the Specialist Roy, face the mutants in a fight to the death. Bloom senses that her sister Daphne is in extreme danger and is trying to contact her telepathically.

Episode 5X10 The Trix want to steal the magic of Christmas from Bloom, since they believe it’s a powerful spell that can increase their powers. At Alfea, the Winx are surrounded by fearsome ice dragons. Will Bloom be able to celebrate Christmas with her family?

Episode 5X11 Daphne is interrogated by Tritannus and the Trix, who want to wrangle out the secret of the Sirenix power. At Alfea, the Specialists’ acrobatics show is ruined by the intervention of the Trix, who with a spell transform the Windriders into terrifying black lions. The Winx, on a mission in the depths of Lynphea, hoping to find the Gem of Courage, find themselves up against a ravenous sea plant.

Episode 5X12 In the palace of Domino, a regal ceremony takes place and the Winx put on their royal garbs, but meanwhile the riddle connected to the third gem is revealed, and Bloom is forced to leave the gathering and go to an underwater place called Great Yellow Barrier. At the bottom of Domino’s ocean, the Winx must conquer their fears and overcome an extreme test of courage.

Episode 5X13 The Winx activate the Source of Lake Roccaluce to open the Sirenix portal, which leads to the Infinite Ocean, but Tritannus goes before them and, with his trident, absorbs the power of the source of the lake, which begins to dry up. The Winx, with the help of their Guardians, do everything possible to restore the Sirenix source, save Lake Roccaluce, and enter the Infinite Ocean. Meanwhile, Tritannus sucks up Daphne’s power and gives it to the Trix, who become stronger than ever and accompany Tritannus in the Infinite Ocean. Tritannus’s plan could be complete very soon. ..

SOURCES: http://unadinoi.wordpress.com/2012/10/12/episodes-8-13-plot-summaries-big-spoilers/

http://www.movietele.it/post/serietv/8796-winx-club-5-nuovi-personaggi-e-trame-degli-episodi
 * It's written in Italian.