Beelzebub, Devourer of Souls

Multiple Heads. Beelzebub gains an additional action per turn equal to the number of heads it has (5). It does not gain additional move and bonus actions. If Beelzebub takes 75 points of damage in one turn, it looses a head.

Reactive Heads. For each head that Beelzebub has beyond one, it gets an extra reaction that can be used only for opportunity attacks.

Innate Spellcasting. Beelzebub's innate spellcasting ability is Charisma (spell save DC 15). It can innately cast the following spells, requiring no components:

At will: detect thoughts

1/day: dominate monster

Devil’s Sight. Magical darkness doesn’t impede Beelzebub's darkvision.

Aversion of Fire. If Beelzebub takes fire damage, it has disadvantage on attack rolls and ability checks until the end of its next turn and cannot utilize its regrowth ability until next turn.

Immutable Form. Beelzebub is immune to any spell or effect that would alter its form.

Rubbery Skin. Whenever the Beelzebub is subjected to lightning damage, it takes no damage and instead regains a number of hit points equal to the lightning damage dealt.

Legendary Resistance (2/Day). If Beelzebub fails a saving throw, it can choose to succeed instead.

Multiattack. Beelzebub can use a claw attack and a bite attack on its turn.

Bite. Melee Weapon Attack:+10 to hit. (3d6 + 5) piercing damage. On hit target must make a Constitution saving throw (DC 15) and take (3d4) Necrotic Damage or half on a successful save.

Claws. Melee Weapon Attack: +8 to Hit to hit., reach 20 ft., one target. On Hit: (3d6 + 10) slashing damage. If Beelzebub succeeds on a claw attack, it can choose to grapple the target instead of dealing damage. (Beelzebub can only grapple one creature at a time and cannot use its claw attack while grappling a creature.)

Engulf. While grappled Beelzebub can engulf the target with one of its heads foregoing an attack. The engulfed target must make a DC12 Strength Save or take (6d4) Acid Damage and remain engulfed. The engulfed target cannot take any actions.

Regrowth. Beelzebub can use a bonus action to begin regenerating a head that has died. It takes three Regrowth bonus actions to fully regrow a head. It regains 25 hit points each time it uses Regrowth.

Dark Lullaby. Beelzebub can use a bonus action to stop singing or to start its song with an additional head.

Multireact. Beelzebub can make two reactions per round as long as it has three or more heads.

Wail. After taking damage, Beelzebub can use a reaction to wail. Creatures within 5ft of Beelzebub when it wails take 2d4 psychic damage.

Beelzebub can take 3 legendary actions, choosing from the options below. It can take only one legendary action at a time, and only at the end of another creature's turn. Beelzebub regains spent legendary actions at the start of its turn.

Bite. Beelzebub makes a bite attack.

Shriek. Beelzebub targets creatures within range of one of its heads and blasts it with a cone of piercing noise. Creatures within a 10 foot cone take 12 (4d6) psychic damage.

Harrowing Scream. (requires 2 actions) All of Beelzebub's heads unleash a scream of fury, pain and sorrow. All creatures the heads can see within 60 ft. must make a DC 18 Charisma saving throw or become frightened and paralyzed until the end of Beelzebub's next turn.