Mylène Haprèle is a student in Miss Bustier's class at Collège Françoise Dupont. In "Horrificator" after feeling humiliated for getting scared easily while filming Nino Lahiffe's movie, she gets akumatized by Hawk Moth and becomes Horrificator, a monster supervillain. In "Gang of Secrets", after Marinette keeps hiding secrets from them, Mylène is re-akumatized by Shadow Moth into Horrifcator along with Reflekta, Princess Fragrance, Timebreaker and Lady Wifi, the five supervillains all form the Gang of Secrets, a group of supervillains who want to reveal Marinette's secrets. In "Mega Leech", in order to defeat Malediktator and his titular sentimonster, Mylène receives the Mouse Miraculous from Ladybug. When the Miraculous is inhabited by Mullo, Mylène becomes Polymouse, a mouse-themed superhero who helps Ladybug and Cat Noir during "particularly difficult missions" in the fourth season and beyond.