He was selected king of all the Goombas. The Goombas picked him to be protected, but the king lied to them all. For at least 30 years he has been slaving the species. Mario declared war with him. He has the power to grow into huge size. It became such a problem actually that Mario had to stop him. He isn't as tough as Mario 318, but he did what he could. Waluigi accepted his opinion in the end, but he knew he could not be alive and thrive as a person any longer for his beliefs.