How can I beat armstrong?

When fighting him while he is in his metal gear, just dodge the lasers, then take out his legs when their vulnerable. Afterwards while fighting him on the destroyed gear, just survive the first time. The second time your supposed to lose. During the final battle keep an eye on the direction he charges and punches a line of explosions toward you. It's best to keep a distance from him while he attacks. When you can, charge toward him and use a slide attack to damage him. He'll jump on top of the rubble around you and throw large vehicles at you, which you destroy by using sword mode to cut along the orange lines on them, and then armstrong's face where you get a chance to do some real damage to him. Healing items are dropped after this which you can use to heal against any damage to you're self. When he crouches and green light surrounds him, get behind him and use sword mode to cut his back. Finally he'll charge at you and you'll just have to follow the button inputs for a satisfying end to the battle.