Fawful, a green-bean like character, is an antagonist that first appeared in Mario and Luigi: Superstar Saga, as a pupil to the evil Cackletta. Fawful's second appearance was when he got a lesser role in the second installment of the Mario and Luigi series, Mario and Luigi: Partners in Time, as only an underground salesman. He posed no threat there. In the 3rd appearance of Fawful, he had the role of the main villain in the most recent Mario and Luigi game, Mario and Luigi: Bowser's Inside Story. He sold Bowser an evil Vacuum Mushroom, causing him to suck up everything in sight, including the Mario Bros., a handful of Toads including Toadsworth, and Princess Peach. Fawful controlled an evil army of Bowser's minions hypnotized by Fawful, including an evil Pig named Midbus. He has also taken up home in Bowser's Castle.
As of now, this is Fawfuls final appearance and roll in a game, but continues to be one of the most well-known antagonists Mario has encountered. (yet)
His most recent appearance was in Mario & Luigi: Bowser's Inside Story.