Bean Fever

Bean Fever is a condition endemic to the Beanbean Kingdom. It causes whoever has it to gradually turn into a bean. Bean Fever can only be contracted by foreigners. It is caused by the consumption of unfamilar beanish food, one known food being the Invincishroom. Mario acquired this terrible disease while in Little Fungitown during Mario & Luigi: Superstar Saga, prompting Luigi to go on a solo mission to find the cure.

Trivia

 * No matter how long it takes Luigi to obtain Crabbie Grass, Mario will not transform into a bean.