Wendigo

 Berserk. Whenever the Wendigo starts its turn with 40 hit points or fewer, roll a d6. On a 6, the Wendigo goes berserk. On each of its turns while berserk, the Wendigo attacks the nearest creature it can see. If no creature is near enough to move to and attack, the Wendigo attacks an object, with preference for an object smaller than itself. Once the Wendigo goes berserk, it continues to do so until it is killed or regains all its hit points.

Regeneration. The Wendigo regains 10 hit points at the start of its turn if it has at least 1 hit point.

Trampling Charge. If the Wendigo moves at least 20 feet straight toward a creature and then hits it with a gore attack on the same turn, that target must succeed on a DC 16 Strength saving throw or be knocked prone. If the target is prone, the Wendigo can make one claw attack against it as a bonus action.

Reckless Attack. The Wendigo can throw aside all concern for defense to attack with fierce desperation. When it attacks on its turn, it can decide to attack recklessly. Doing so gives it advantage on melee weapon Attack rolls using Strength during this turn, but Attack rolls against it have advantage until its next turn.

Keen Smell. The Wendigo has advantage on Wisdom (Perception) checks that rely on smell.

Eldritch Horror. Once a day, when transforming into the Wendigo, you can use this feature to cause all humanoid creatures within 30 ft to succeed on a DC 16 constitution saving throw or be frightened for 1 minute. This feature cannot be used until the next day. 

Multiattack. The Wendigo makes two attacks, either with its Claws or its Gore.

Claws. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 27 (4d10 + 5) slashing damage.

Gore. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 23 (4d8 + 5) slashing damage.

Soul Drain. Melee Weapon Attack: +6 to hit, reach 10 ft., one creature. Hit: 23 (3d12 + 3) necrotic damage. The Wendigo heals for half of the damage done by this attack. The target must succeed on a DC 15 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.