An Evil Prophecy from Time Immemorial
In Super Paper Mario, we see that Luigi is not only a bad guy, he’s the crux of an evil prophecy. The most definitive piece of proof that in Luigi’s green heart lurks the potential to destroy not just the Paper Mario World… but all worlds.

Nintendo
We see hints of this right from the game’s start. Where Luigi is clearly seen inviting chaos and hoping to endanger his brother.

Nintendo
Early on in Super Paper Mario, Luigi is (allegedly) captured and brainwashed. The game’s antagonist, an interdimensional being known as Count Bleck, turns Luigi into a bandana sporting henchman known only as ‘Mr. L’. The villain also has knowledge of a book of prophecies: The Dark Prognosticus. The ancient tome speaks of “the man in green”. A man who is fated to bring about the end of all existence. The Light Prognosticus also found in the game was supposedly written as a solution to the problem of the utter destruction of the universe as told in the Dark Prognosticus. The implication being that the text, foretelling the Man in Green’s path of evil, is the true, original version.

Nintendo