Story related, cannot be missed.
You will nab this achievement pretty early in the game. Simply traverse the icy plains and follow the linear path up and up til you reach the top. There you will have an encounter with the Crowfather, whom after a cutscene will appear as a dark version of War for you to fight. He attacks in combos of 3, dodge these then you can get in a quick combo before he blocks and begins another round of attacks. Rinse and repeat until The Crowfather is slain, the achievement should pop after the cutscene of his death.