Sigdis Gauldurson will rise out of a coffin. Make sure to get at least one hit on him so that you will be able to tell which one is he later on. Sigdis Gauldurson will vanish right after he has stood up fully and four f him will appear behind you on different raised platforms above the small lake. If you successfully took some of Sigdis Gauldurson's health you will easily be able to tell which in is the real one because he will be the only one with less than full health. They perform annoying force shouts that will cause you to fly around the place, don't worry it won't instant kill you. You willl have enough time to get a few hits on him before he will disappear again. Keep finding him based on his lowered health.

If you find that you are taking too much damage I do suggest that you go and kill the copies, I am pretty sure he won't disappear until you have dealt at least some damage to him. If you find that is incorrect feel free to leave me a comment below so that I and other people know as well.