He is nervous. Very very extremely nervous. Very extremely nervous. So don't disturb him. He developed a quick jerking motion in self defense. Whenever he is near danger, he abruptly pulls back. While fighting, he inflicts hundreds of small wounds very rapidly that slowly drain your hero's stamina. He twitches so fast that it is almost impossible to hit him. Your best bet is to fight him near a cliff, wherr he might accidentaly twitch backwards and fall off.