While most PE villains have a motive or goal they wish to achieve, some commit their heinous acts purely out of sadism and personal pleasure or just enjoy being evil. Various incarnations of the Joker abide by this motivation, but there are other examples. Invictus, for instance, doesn't appear to have any clear reasoning for wanting to completely destroy the multiverse but given how sadistic it is towards Gary and the rest of the Team Squad, it likely just does so out of cruel amusement. Yuuki Terumi also admits that he doesn't have much of a real reason for his crimes and considers misery "interesting". There are likely others, but I want to hear from you all.