Belos, Soul-beast

Regenerator: Belos, Soul-beast will revive 3d8 hours after being defeated for the first time. Once revived, this ability will be inactive until 2d20 days pass.

Gooey: Belos, Soul-beast is resistant to slashing, bludgeoning, and piercing damage.

Soul Stealer: When hitting a non-undead creature with a melee attack, Belos, Soul-beast rolls 4d4 and regains that amount of hit points.

Legendary Resistance (1/Day). If Belos, Soul-beast fails a saving throw, it can choose to succeed instead.

Mind control (Recharge 12): Belos, Soul-beast may use it's action to fling some of it's gooey self at a creature within 60 feet. This is treated as a ranged attack. If hit, the creature must make a DC17 CON and a DC17 WIS save. If both saves fail, the creature falls under the effects of Dominate Person, and must follow the commands of Belos. Each turn, the creature can make a DC20 WIS check, on a success the creature is freed from Dominate person and takes 3d8 acid damage. If only one of the saves fail, the creature loses 10 feet of speed and gains disadvantage on all saving throws and attack rolls. This condition remains until the creature succeeds at the saving throw, which they can reroll each turn. If both saves succeed, nothing happens.

Claw slash: Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 2d8 + 5 slashing damage. 

Dominating sight: Ranged Magic Attack: +9 to hit, range 60 ft., two targets. Hit: 3d6 psychic damage. On hit, the target becomes frightened until the end of their next turn.

Soul-searing Strike: As a bonus action, Belos, Soul-beast may spend 10 of its hit points to empower its next attack with the blue flames of burning souls. This adds 2d8 necrotic damage to the next attack made by Belos, Soul-beast.

Repelling roar: When hit by a creature closer than 20 ft, Belos, Soul-beast can emit a repelling blast of energy in a 40 foot radius sphere around itself. Any creature caught within this sphere must make a DC18 dexterity saving throw or be pushed 10 feet away from Belos, Soul-beast.

Belos, Soul-beast can take 3 legendary actions per day, choosing from the options below. Only one action can be used at a time, and can be used on any creatures' turn.

Sludge Shield: Belos, Soul-beast negates 30 damage from any incoming attack. If 30 is greater than the total damage of the attack, the attack is stopped and Belos, Soul-beast takes no damage from it.

Ooze Shackles: Shackles made of sludge are summoned to restrain any medium or smaller creature that Belos, Soul-beast can see within 60 feet. The target creature must make a DC19 strength saving throw, or fall prone until the end of their next turn.

Palisman-Eater: Belos, Soul-beast may make a grapple check against any creature wielding a staff within range. If the grapple succeeds, Belos, Soul-beast will damage the Palisman of the staff used by the creature. Belos regains 2d6 + 8 hit points, and the affected creature has disadvantage on all spellcasting until a long rest is completed.