The Mysterious Berserker

You'll start this quest by needing to speak with Bjorn. He's located in a cave south of Northwic, within East Anglia. If you're having trouble finding the cave entrance, which is quite large, use your raven to scout the area. Once you find Bjorn, listen to what he has to say. He wants you to prove yourself by hunting with his white bear, Njal. If Njal trusts you, Bjorn might consider helping you.

After speaking with Bjorn, follow Njal the bear through the cave and then south along the river. When you reach the riverbank, you'll need to catch some Bullhead fish to feed Njal. You can use Odin's Sight to spot them easily. If you have the fishing line, it'll be simpler, but if not, you can shoot them or use your melee weapons on fish in shallow water. You only need to catch one, then speak with Njal.

Once Njal has eaten, you'll be tasked with taking down some Mercian soldiers. They'll attack from the fields to the southeast, so be prepared. Watch out for the two skirmishers among them; they're tricky to hit. The best way to deal with them is to dodge their attacks first, then immediately follow up with a light or heavy attack, which will almost always land.

After defeating the first group of soldiers, return to Bjorn outside the cave to the north. He'll need your help against another group of Mercian soldiers. This group includes archers, more skirmishers, and a Goliath elite. The Goliath has weak spots on its left hand and left leg. Aim for these spots with your bow to make it vulnerable to a stun attack, which deals significant damage. Alternatively, Bjorn can tank the Goliath while you wittle its health down with regular attacks.

Once all the soldiers are defeated, speak with Bjorn. A cutscene will play, and the quest will be completed.