The second is Sigdis Gauldursun. He will spawn three copies of himself around elevated positions around the room. You will just have to find the real one by hitting every one of them. The fake one's will die instantly. Once you have dealt a little damage to Sigdis just look around the room until you find the version of Sigdis that has taken a little damage. If you find that you are taking a lot of damage be sure to kill all the fake Sigdises.