Bellum

Flailing Tendrils. Bellum has five tendrils. If a tendril is hit by an attack that specifically targets it, Bellum takes no damage, but the tendril is stunned. At the beginning of each of Bellum's turns, 1d4 tendril(s) recover(s) from being stunned.

Legendary Resistance (3/Day). If Bellum fails a saving throw, it can choose to succeed instead.

Multiattack. Bellum makes a number of Tendril Strikes equal to the number of tendrils that are not stunned, or two Bite Attacks.

Tendril Strike. Melee Weapon Attack: +14 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage . 

Bite Attack. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 21 (2d12 + 8) piercing damage. 

Bellum 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. Bellum regains spent legendary actions at the start of its turn.

Wriggle Away. Bellum moves up to 120 ft. This movement does not provoke opportunity attacks.

Horrifying Vision. All creatures within a 60 ft cone originating from Bellum's central eye must make a DC 18 CHA saving throw. On a failed save, a creature takes 19 (6d6 + 4) psychic damage and becomes frightened of Bellum. On a successful save, creatures take half as much damage and do not become frightened.
Creatures frightened by Bellum in this way may make a DC 18 CHA saving throw at the end of each of their turns to end the effect; if they are greater than 60 ft away from Bellum, they roll at advantage.. 

Life Force Drain (Costs 2 Actions). Melee Spell Attack: +10 to hit, reach 20 ft., 1 target. Hit: 32 (8d6 + 4) damage. Bellum recovers hit points equal to half the amount of damage dealt. The target's maximum hit points are reduced by the amount of damage dealt. If this attack reduces the target's hit point maximum to 0, the target is petrified. This reduction to the target's hit point maximum lasts until the target completes a long rest.