Mirror of Truth is a magical mirror mentioned by Miss Faragonda in season 3. According to Miss Faragonda, it helps you turn back to your old self again.
Season 3; How it worked on StellaEdit
As Stella was turned into a green, fat, blonde monster, (mon - stella) miss Faragonda said that the Mirror of truth will help her a lot to turn her back to her old self again. Before finding the magical mirror, Stella was afraid that Brandon would see her with disgust, so Flora thought of a plan. Flora had put a spell to Stella so that Brandon would see her as her old self. As the winx and the specialists were finding the Mirror of Truth, Brandon told Stella straight ahead that Flora's disguising spell did not actually work on him. Stella was really upset. Brandon told her that he still loves her to comfort her. As they found the Mirror of Truth, Stella wishes to be her old self again. The mirror refused because she is not worth fighting for. When Stella was crying, her tears brought her perseverance and confidence which is enough to turn her back to normal. The winx girls and the specialists returned happily as they see Stella being her old self again.