Ancient Shoosuva

Ancient Beast. The thick magical fur of the ancient beasts give an advantage on saving throws against magic attacks and is immune to crits. It also cannot be moved against it's will.

Legendary Resistance (4/Day). If Lagrigoyi's bane fails a saving throw, he can choose to succeed instead.

Terrifying presence. The first time a creature comes within 30ft of the ancient shoosuva must make a DC 27 wisdom save or become frightened for 1 hour. If the creature makes any wisdom save caused by the ancient shoosuva, it becomes immune to this effect for 24 hours. If a creature under the effect of Terrifying presence gains the frightened condition from any other source, it becomes terrified an must use all it's turn to run from the Shoosuva as far as possible.

Keen senses. The Ancient Shoosuva has advantage on perception checks.

Multiattack. The ancient shoosuva makes three rend attacks and one Tail Stinger attack. It can replace one attack with a consume.

Rend. Melee Weapon Attack: +19 to hit, reach 5 ft., one target. Hit: 36 (4d12 + 10) slashing damage. Once per turn it does piercing instead.

Tail Stinger. Melee Weapon Attack: +19 to hit, reach 15 ft., one creature. Hit: 21 (2d10 + 10) piercing damage, and the target must succeed on a DC 27 Constitution saving throw or become poisoned. While poisoned in this way, the target is also paralyzed. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Consume. Melee Weapon Attack: +19 to hit, reach 5 ft., one target, must have Incapacitated condition or dead. On a hit the Shoosuva heals 4d10+10 hp and the creature dies and it's body is destroyed. 

Rampage. When it reduces a creature to 0 hit points with a melee attack on its turn, the shoosuva can move up to half its speed and make one rend attack.

Haunting howl. The Ancient Shoosuva howls, every creature that can hear in a 30ft emanation makes a DC 27 Wisdom save or be frightened. it can repeat the save at the end of it's turn. If saved the creature is immune for 24 hours.

The Ancient Shoosuva gets 3 legendary actions per turn

Pounce. The Ancient Shoosuva can move up to half its Speed, and it makes one Rend attack.

Monstrous glare. A creature within 5ft of the Shoosuva must make a wisdom save DC 27 or become frightened. 

Tail swing. Melee Weapon Attack: +19 to hit, reach 5 ft., one target. Hit: 17 (2d6 + 10) bludgeoning damage and be knocked prone.