Fields of the Eternal Hunt, Halls of Valor (Dungeon)
Retains its original name after taming. The runes on Fenryr's flanks glow when he runs. He can only be tamed after you defeat him in Mythic mode, and only if you solo the dungeon up to, and including, that fight. That means you must also solo the first boss of the dungeon (Hymdall) as well as Fenryr. The tameable version of Fenryr spawns at the back of his den after you defeat him.
Level scaling: Most NPCs will scale with the Hunter's level, within the constraints of their level range. Hunters can tame regular NPCs up to 2 levels higher than them, but can only tame elite NPCs of the hunter's level or below.