I can honestly say that I don't think I'll ever be into Winx Club, but I do like to listen to Thomas Vaccaro video essays while I work. So after listening to his video on Witches in Winx I made a trio of not directly hostile witches inspired by fairy tales.
Margaretta, The Candy Witch, was abandoned by her parents along with her baby brother as a child. The two of them were taken in by a witch, who happened to run a multidimensional magical sweets shop, in return for Margaretta becoming her apprentice.
Willa, The Witch of Dance, was a peasant girl from Melody who fell in love with a nobleman's son, only to discover that the son was already betrothed and their entire relationship had been a cruel prank to amuse his fiance. In revenge, she used dark magic to make the entirety of the nobleman's court dance nonstop, until a nearby guardian dispelled the curse and sent Willa to Cloud tower.
Mariana, The Witch of the Depths, was born at the very bottom of Andros underwater kingdom, a world completely devoid of light. Tired of feeling isolated, she swam up to the surface and was immediately ostracized by her fellow mermaids for her ugliness. Luckily for her, she has an incredible talent for magic, and gave herself a pair of legs so that she could find a world that would accept her.
Winx fans tell me if I got any of the lore wrong, I know there is a new show that retcons Cloud tower, but if there are any other inconsistencies feel free to share.
shout out to @tvaccaro for great world building analysis <3