Chernabog The Dark God

Empowered Attacks. Chernabog's attacks and the attacks
of his conjured minions are treated as magical for the
purpose of bypassing resistance and immunity to
nonmagical weapons.

Discorporation. When Chernabog drops to O hit points or
dies, he retreats back into his mountain, and he is unable
to take physical form for a time.

Divine Spellcasting. Chernabog's innate spellcasting
ability is Charisma (spell save DC 27, +19 to hit with
spell attacks). He can innately cast the following spells at
9th level, requiring no components:

At will: counterspell, dispel magic, finger of death,
hellish rebuke (within 300 ft.), hold person

3/day: divine word, power word kill, power word pain,
power word stun, storm of vengeance

Immutable Form. Chernabog is immune to any spell or effect that would alter his form. 

Legendary Resistance (5/Day). If Chernabog fails a saving
throw, he can choose to succeed instead.

Limited Magic Immunity. Chernabog has advantage on saving throws against all other spells and magical effects.

Sunlight Sensitivity. While in sunlight, Chernabog has
disadvantage on attack rolls and on Wisdom
(Perception) checks that rely on sight. He also in unable
to regain hit points while in direct sunlight.

Rooted. Chernabog automatically succeeds on all
Strength saving throws and cannot be knocked prone.

Chernabog can take 5 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. Chernabog regains spent legendary actions at the start of his turn.

Spell. Chernabog casts a spell or uses Dark Sacrifice.

Fire Breath (Costs 2 Actions). Chernabog breathes fire in a 90-foot cone. Each creature in that area must make a DC 27 Dexterity saving throw, taking 91 (26d6) fire damage on a failed save, or half as much damage on a successful one.

Wing Attack (Costs 2 Actions). Chernabog beats his wings. Each creature within 60 feet of Chernabog must succeed on a DC 27 Dexterity saving throw or take 49 (6d12 + 10) bludgeoning damage and be knocked prone.

Sweep (Costs 3 Actions). Chernabog makes a slam attack against each creature within 60 feet of him.