Very useful for raising wyverns and drakes because fenrir's inventory acts like a preserving bin/fridge making the milk or venom last 2 days in its inventory
Only one person in the fight will get a cryo pod with a Fenrir in it once the boss dies, and the level depends on which difficulty fight you pick. (On official)
Fenrir close to direwolves cause the direwolves' eyes to glow, and gives them a buff which reduces incoming damage by ~12.5% and increases damage output by ~25%. This buff can stack with mate boost, pack bonus, howl, and yuti roar.