Field of the Eternal Hunt, Halls of Valor (Dungeon)
Runes on flanks glow when running. Available by soloing Mythic only. Fenryr isn't tameable until after defeat, so you must solo defeat Mythic Hymdall and Mythic Fenryr for the tameable version of Fenryr to appear.
*Level scaling: In Shadowlands 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.