Maerd: OK, here is a solution for those who cannot kill it.

******SPOILERS********


Right after the Selkirk's ghost leaves your body there is a draugir that you will fight but it doesn't attack till you come closer. So, have ~20 claw traps (or other traps in large quantities) in your backpack (collect them at chapter 1 very easy) and set them all on the spot where you are standing.

Then attack draugir, defeat him. As soon as draug appear cast quen and run to your traps. Position yourself so that the traps are between draug and yourself. Wait for him to charge. He charges into the traps... instant kill :)

If you are trying yrden + attack from the back there is a bug. It seems like draug is always turning to face you but it is just an animation, which doesn't correspond to the actual situation. If you attack the spot where its back side must be (even though it looks like a frontal attack) you will deal double damage bypassing a shield.

To prevent draug from calling catapults and archers stay close to him and attack. It never calls support when you are slashing it with your sword.