Easy Supercharge:

There is a way to quickly fill up the weapon gauge that allows you to do a supercharge attack. Deflect enemy fire with the sword attack (tap B). They will drop green items you can pick up (press Down + B) that will quickly fill the weapon gauge. Once the gauge is flashing you can do the supercharge attack by tapping R(2).
Defeat Green without having him transform

Green can be easily beaten. He was made so he can only transfrom when your chracter is not looking at him. Simply have your character keep looking at Green and fire and youll easily beat him without having to deal with his transformed states.