The Clown Prince of Crime decides Thor needs a dose of insanity added to his life. Thor is unaware of any attack against him. Joker is allowed 2 months prep time, in which he can steal whatever resources he needs or find people to help him. If Joker tries to find someone that can help, they have to be reasonably convinced. No saying, "Oh, Joker just gets Superman" because Superman obviously wouldn't just go help Joker. Joker has intel on anybody close to Thor he could kidnap or blackmail against Thor with. Thor wins by utterely obliteratong Joker, Joker wins by either KO, Death, or Situational Circumstances (i.e. Thor must surrender or a city of people die). Can the Madman do it?