Fenrir

Primal Magic: Fenrir's attacks are magical, and deal 4d8 additional necrotic damage (included in the attack).

Immutable Evil: Fenrir has advantage on saving throws against spells and magical effects, and he is immune to any effects that would alter his form or banish him from his current plane.

Death Throes: When Fenrir falls to 0 hp, he can immediately use his Furious Howl one last time.

Regeneration: If Fenrir has at least 1 hit point, he regains 50 hit points at the start of his turn.

Legendary Resistance (5/day): If Fenrir fails a saving throw, he can choose to succeed instead.

Actions

Multiattack: Fenrir can use his Frightful Presence. He then makes four attacks, one with his bite, and any combination of three Claw and Bristle Spike attacks.

Bite: Melee weapon attack: +17 to hit, reach 10ft, one target. Hit: 28 (3d12+9) slashing damage plus 18 (4d8) necrotic damage. On a hit, the target is grappled (escape DC 25) in Fenrir's mouth. Until the grapple ends, the target is Restrained. Fenrir automatically hits with this attack against a creature he is grappling.

Claw: Melee weapon attack: +17 to hit, reach 15ft, one target. Hit: 18 (2d8+9) slashing damage plus 18 (4d8) necrotic damage.

Bristle Spike: Ranged weapon attack: +14 to hit, reach 60/120ft, one target. Hit: 13 (2d6+6) piercing damage plus 18 (4d8) necrotic damage. The target must succeed on a DC 20 Constitution save or be Poisoned for 1 minute. If the target fails their save by 10 or more, they are also Paralyzed.

Frightful Presence: Each creature of Fenrir's choice that is within 120 feet of Fenrir and aware of it must succeed on a DC 22 Wisdom saving throw or become Frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to Fenrir's Frightful Presence for the next 24 hours.

Furious Howl (recharge 5-6): Fenrir lets out a howl that can be heard for many miles. All creatures within 300 feet must make a DC 20 Constitution saving throw. On a failed save, they take 45 (10d8) psychic damage and are Stunned until the end of Fenrir's next turn. On a success, they take half the damage and are not Stunned.

Legendary Actions

Fenrir can take 5 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Fenrir regains spent legendary actions at the start of its turn.

Attack: Fenrir makes a Claw or Bristle Spike attack.

Leap (2 actions): Fenrir jumps up to 60 feet without provoking opportunity attacks to an unoccupied space he can see. All targets within 10 feet of the impact must make a DC 22 Dexterity saving throw or take 4d6 bludgeoning damage and be knocked Prone.

Bristle Volley (3 actions): Fenrir makes a Bristle Spike attack at every creature within 60 feet of him.