When you first get into the room where you fight SA-X, charge your Power Beam and go up to the door. Stay with ground combat. Since it is charged, keep it like that and wait until he is normal (and not a green ball and invulnerable). Take the first shot, then hold it down to charge again. He should jump into the air and land next to you. This is your chance to shoot. Do the same thing repeatedly until he gets fuzzy. When you hit him he will turn into a giant monster. The only way he can hurt you is to jump on you. Charge up your beam and hit him in the face four times. His eyes will go red. Walk next to him and he will die. On the spikeball, charge up your missiles, When his eye opens up, shoot then jump over him immediately. If you run low on health, use your Screw Attack and hit him. A group of Xs will appear. Collect as many as needed. You can do this repeatedly.