In the level cirith angol at the end you will have to fight gorbag. Then don't run up to him. Run to the spears and press z to pick them up and throw it at his sheild. Then throw another at him to make him dizzy. Then instead of throwing another at him run up to him and hit him. When he falls down, quickly stab him (R). He will get up for another sheild. Repeat this to beat gorbag.