Bonding is a power introduced in Season 2.
Bonding is a phenomenon where a strong connection is created between two magical creatures, whether it be emotional or empathic. From the very moment two creatures bond, they become almost like family, and their powers are strengthened, sometimes to such a degree where their magic is increased exponentially. In some cases, bonding can even restore magical energy to one of the creatures involved.
In "The Shadow Phoenix," Concorda meets Bloom and tells her about bonding. It is a deep, somewhat rare connection between fairies and pixies. It is a bit like falling in love, and the two become inseparable, just like twin sisters. Concorda says it is a very special thing. She also reveals that she is bonded to the Magic Archive.
In "Magic Bonding," the captured pixies rejoin Aisha with her new friends, Bloom, Stella, and Sky. Stella bonds with Amore and Bloom bonds with Lockette. Aisha explains bonding as "love at first sight" to Sky.
In "The Mysterious Stone," the rescue group and the pixies arrive at Alfea and join the Winx. Three pixies bonded with the Winx on the spot. Digit, who had met Tecna in a chat room prior, finally meets her face-to-face. Tune and Musa bond over sense of style, and Chatta gossips to Flora.
In "The Shimmering Shells," in the oceans of Andros, Aisha meets Lemmy and bonds with her, restoring Lemmy's powers. Lemmy tells the Winx that she is the keeper of the Andros Gate, and that Tritannus forced it open and stole her powers. In hopes to rid the ocean of Tritannus' evil, the group makes their way to the Labyrinth of the Abysses. Later, in the oceans of Solaria, Stella meets Illiris and bonds with her, restoring Illiris' powers. As the keeper of the Solaria gate, Illiris leads the Winx and Lemmy to the Azure Valley to the light of the deeps.
In "Secret of the Ruby Reef," in the oceans of Melody, Musa, who Tritannus turned into a monster, bonds with Sonna, keeper of Melody's ocean gate, both breaking the spell on Musa and restoring Sonna's powers.
In "The Gem of Empathy," in the oceans of Zenith, a panicked and powerless Lithia, keeper of the Zenith gate, runs up to the Winx and Roy. Tecna calms her and bonds with her, restoring Lithia's powers. Lithia then leads the Winx to Data Bridge Castle.
In "Trix Tricks," in the oceans of Linphea, the Winx locate Desiryee, keeper of Linphea's ocean gate, who Flora bonds with, restoring her powers. She then leads the Winx and their selkies to the Flower of the Depths.
The Shadow Phoenix
Bonding is only mentioned briefly during the pixies retelling of major events in Monsters on the Loose when Lockette, Amore, Chatta, Tune and Digit talk about how they were able to bond with Aisha's new friends, the Winx Club.