The troll, Jarn Fotr is similar to the other trolls you faced before. It’s still a safe option to keep your distance and pummel it with axe throws, ranged runic attacks, and arrows. Keep an eye out of its frost area attacks since it will cause the freeze status that will slow you down on top of dealing considerable damage to you. It will be better to use your runic attacks after Atreus fires all of his light arrows so you can deal extra damage from the light arrows’ weakening effect.
The troll’s attacks are very slow and predictable so you shouldn’t have problems evading them. About halfway down its HP, it will call in reinforcements in the form of explosive and fire draugrs. Use the large battlefield to keep your distance and even luring the troll in catching the draugrs in a crossfire with its attacks. When it’s almost down, you can use your Spartan Rage to pummel it to submission and finish off the job. After defeating the troll, loot a Frozen Flame, The River of Knives (heavy runic attack), and Solid Svartalheim Steel from it.