Wendigo

Magic Resistance. The Wendigo has advantage on saving throws against spells and other magic effects.

Weird Sight.  The Wendigo has truesight and can see into and out of the Ethereal Plane.  Its Howl, Surge of Hunger, and Swallow Heat abilities can affect creatures in the Material Plane even when the Wendigo is in the Ethereal Plane.

Avatar of Hunger.  The Wendigo itself is overwhelmed with hunger, and it won't stay in the Ethereal Plane for longer than 1 round if prey is nearby.

Enigma.  The Wendigo is immune to any divination spells to read its mind or gather information about it.  It is immune to mind-affecting spells and effects.

Legendary Resistance (3/day). When the Wendigo fails a saving throw, it can expend a Legendary Resistance to automatically succeed instead.

Cold Hunger.  The Wendigo's attacks can afflict a creature with Cold Hunger, which is considered a curse. 

• A creature can repeat the saving throw when it finishes a long rest, and the Cold Hunger curse ends only after the saving throw is successful three times.  Casting Remove Curse or Greater Restoration allows the creature to attempt a saving throw against the curse, which counts toward the three successes needed to end the curse.
• The creature feels a cold numbness and a wavering urge to eat people.  The creature is immune to cold damage and the effects of a cold climate, but they still suffer cosmetic damage from frostbite. 
• When the creature finishes a long rest while afflicted by the curse, they lose 2d4 Wisdom, or they only lose 1d4 Wisdom if they have consumed the flesh of a humanoid within the last 12 hours.  The creature recovers 1d4 Wisdom damage each day after the curse ends, or they can recover 1d4 Wisdom damage from each casting of Greater Restoration once the curse ends.  The Wisdom damage can't be recovered while the curse is still active.

Multiattack. The Wendigo can make two Claw attacks.  It can then make a Bite attack or use its Howl.

Claws. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 21 (3d8 + 8) slashing damage and 13 (3d8) cold damage.  Instead of dealing the slashing damage, the Wendigo can grapple the target.  A creature struck by the claws must succeed on a DC 15 Constitution saving throw or be afflicted with Cold Hunger.

Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 21 (3d8 + 8) piercing damage and 22 (5d8) cold damage.  Instead of dealing the piercing damage, the Wendigo can swallow a creature that is Large or smaller.  While swallowed, a creature is blinded and restrained, and takes 9 (2d8) acid damage and 9 (2d8) cold damage at the start of each of its turns.  If 30 or more damage is dealt to the exposed entrails of the Wendigo in a single round, the swallowed creature is released.

Howl (recharge 5-6).  The Wendigo lets loose an unnatural, terrifying howl, audible for up to 10 miles.  Each creature of the Wendigo's choice that can hear the howl must succeed on a DC 19 Wisdom saving throw.  On a failed save, a creature is frightened of the Wendigo and of cold weather for 1 hour.  While frightened this way, the creature has vulnerability to cold damage, and their movement speed is reduced by half.  If the creature cannot see the Wendigo and they are exposed to warmth, once per round they can repeat the saving throw, ending the effects on a success.

Unsettling Presence.  Each creature that can see the Wendigo that is frightened of it must succeed on a DC 15 Constitution saving throw or suffer 1d6 Wisdom damage.

Surge of Hunger. If a creature that the Wendigo can see rolls a critical failure on an attack roll or saving throw, the Wendigo can use its reaction to force that creature to attempt to grapple and eat a humanoid within 5 feet, if able.  The target of the unfortunate creature's surge of hunger must succeed on a DC 18 Strength saving throw or suffer 13 (3d8) piercing damage.  The attacker regains hit points equal to the damage dealt, but must roll a DC 15 Constitution saving throw or be afflicted with Cold Hunger.

Blizzard Gust.  If a creature makes a ranged attack roll against the Wendigo that would hit, the Wendigo can use its reaction to conjure a burst of chilling wind.  The Wendigo's AC increases by 6 for that attack, potentially causing the attack to miss.

(1)  It Appears.  The Wendigo shifts from the Ethereal Plane into the Material Plane.

(1)  You Blink and It's Gone.  The Wendigo shifts from the Material Plane into the Ethereal Plane.

(1)  Maul.  The Wendigo makes a Claw attack.

(1) Swallow Heat.  Each fire within 120 feet of the Wendigo is immediately extinguished, all water immediately freezes, and the temperature in the area drops below freezing if it is not already.  The Wendigo gains resistance to fire until the start of its next turn.

(2)  Frigid Tempest.  The Wendigo transforms into a tornado of snow and ice until the start of its next turn, then it moves up to 60 feet in a straight line without provoking attacks of opportunity, and each creature in its path must succeed on a DC 19 Constitution saving throw or suffer 13 (3d8) cold damage.  While transformed into the frigid tempest, the Wendigo has resistance to all damage except fire damage and it can move through enemy spaces and can move through a space as small as 1 inch.

(3)  It Calls.  The Wendigo immediately recharges its Howl and uses it.