How do you defeat giant plant monster in ben 10 protector of earth

In order to destroy Vilgax, you have to destroy the machine on the left side of him. This should make him smaller. After that the quickest way to win is to attack X,X,A as wildvine until he returns to his previous size. Don't forget there is another machine on the right destroy that should make him return to the smaller size, but have new attacks, so you should keep the X,X,and A controls with wildvine.