A potent front-line unit with solid base Stats and decent Stat Growths mainly focused on Health, Strength and Speed, their only real weakness is a lack of Lust Resistance. With natural Armor and slashing attacks that cause Bleeding, there's no reason not to get one of these easily acquired Special Hybrids.
Their unique skill, StalkPrey, will move the Fenrir to a Bleeding target and remove Defending from it, leaving it open to attack. Additionally, if the Fenrir was in ShadowForm when using it, ShadowForm is replaced with a Strength Buff. This skill has a long range of 6 and costs no AP, so any enemies that are Bleeding will find it impossible to run from a Fenrir.
They start combat in ShadowForm and have a high chance to acquire MistForm to use with the above skill, and Claws to inflict Bleeding if they have a weapon that doesn't let them do so. Curse rounds out their possible skillset by further weakening their enemies.
However with only one fixed skill, there's plenty of room to change things up. If you make one using a Shadow Beast could get BackStab, while using a Vampire could get you DrainCurse. Either one could also get you DrainShadow. Any of these would give your Fenrir even greater offensive capabilities.
They have Heightened Sense which gives a bonus to scouting.