When fighting Pinnacle, repeatedly press JUMP to easily dodge his attacks. Jack will automatically turn to face Pinnacle before he jumps -- don't worry about getting too far away from him. While Jack is jumping, he is impervious to all of Pinnacle's attacks. Do this repeatedly to tire Pinnacle out, then jump on his back and finish him off. You can also attack Pinnacle in front by punching and using low kicks, but this is not recommended since it does not take much damage from Pinnacle.