Mylène Haprèle is a student in Miss Bustier's class at Collège Françoise Dupont.[2] 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", Mylène will get the Mouse Miraculous and will become Multimouse, a mouse-themed superhero.