Wendigo

Ambusher. The Wendigo has advantage on attack rolls against any creature it has surprised.

Mimicry.  The Wendigo can mimic any sounds it has heard.  A creature that hears the sounds can tell they are imitations with a successful DC 15 Wisdom (Insight) check.

Shadow Stealth.  While in dim light or darkness, the Wendigo can take the hide action as a bonus action.

Wendigo Psychosis.  Any creature hostile to the Wendigo that starts its turn within 15 feet of the Wendigo must make a DC 13 Wisdom saving thro, unless the Wendigo or creature is incapacitated.  On a failed save, the creature is frightened until the start of its next turn as images of the target killing and devouring its companions cloud its mind.  If a creature's saving throw is successful, the creature is immune to Wendigo Psychosis for the next 24 hours.

Multiattack. The Wendigo makes two attacks, one with its claws and one with its bite

Claw. Melee Weapon Attack: +6 to hit, reach 5 ft., 1 target. Hit: 11 (2d6 + 4) slashing damage.

Bite.  Melee Weapon Attack:  +6 to hit, reach 5 ft., 1 target.  Hit:  13 (2d8 +4) piercing damage.  On a hit, the target must succeed on a DC 13 Constitution saving throw or take an additional 9 (2d8) necrotic damage.

Wind Walker.  As a standard action, the Wendigo becomes incorporeal until the start of its next turn.  It can can take the Disengage or Dash action as part of this ability, and its jump distance is doubled for the turn.

Shadow Stealth. While in dim light or darkness, the Wendigo can take the Hide action.