Wendigo

Mimicry. The wendigo can mimic animal sounds and humanoid voices. A creature that hears the sounds can tell they are imitations with a successful DC 18 Wisdom (Insight) check.

Cannibilize. When the Wendigo reduces a living creature within 5ft of it to 0 HP, it can use its bonus action to start consuming the corpse of the creature. When it does it regains HP equal to the consumed creture's Constitution score.

Spider Climb. The Wendigo can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Mask of the Wild. The Wendigo can attempt to hide even when it is only lightly obscured by foliage, heavy rain, falling snow, mist, or other natural phenomena.

Innate Spellcasting. The Wendigo's Spell Casting Ability is Wisdom (Spell Save DC 18, Spellcasting attack modifier +9). The Wendigo can innately cast the following spells, requiring no material components:

At Will:  Frostbite, Minor Illusion, Ray of Frost
3 per Day: Fog Cloud, Ice Knife, Misty Step, Ray of Sickness, Silent Image
1 per Day: Elemental Bane [cold], Ray of Enfeeblement 

Multiattack. The wendigo makes three attacks: one with its bite and two with its claws. If it can, wendigo uses its Staggering Roar instead of a Bite attack.

Bite. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 8 (2d4 + 5) piercing damage and 11 (3d6)  necrotic damage. The wendigo regains hit points equal to necrotic damage dealt, unless the target is a construct or undead.

Claw. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 8 (2d4 + 5) slashing damage plus an additional 4 (1d6) cold damage. If the target is a Large or smaller creature that the Wendigo already hit with two claw attack this turn, the target is grappled (escape DC 20). Until this grapple ends, the creature is restrained and the Wendigo can't use its claws against another target. At the start of each of the grappled creature's turns, it takes another 4 (1d6) cold damage.

Staggering Roar (Recharge 5-6). The wendigo emits a thundering roar. Each creature within 30 feet of the Wendigo must succeed on a DC 18 Wisdom saving throw or take 18 (4d8) psychic damage and be stunned 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.

Unnerving Howl. When the Wendigo damages a creature it can let out a horrific cry as a bonus action. Creatures within 30 feet of it must make a DC 18 Wisdom saving throw. On a failed save they are frightened of the Wendigo until the start of its next turn. If the target's saving throw was successful, or if the effect ends on it, the target is immune to the Wendigo's howl for 1 hour.

The Wendigo can take 3 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. The Wendigo regains spent legendary actions at the start of its turns: 

Attack. The Wendigo lunges out and makes one claw attack.

Misty Step (Costs 2 Actions). Disappearing in a shroud of silvery mist, the Wendigo teleports 30 feet to an unoccupied space it can see.

Cantrip. The Wendigo casts one of its cantrips.

Unnerving Howl. When the Wendigo recieves damage, it can use its reaction to use its Unnerving Howl.