Discorporation. When Abzu drops to 0 hit points or dies, his body is destroyed but his essence travels back to the Abyss and is unable to take physical form for a time.

Innate Spellcasting (3/Day). Abzu can innately cast divine word (spell save DC 24). His spellcasting ability is Wisdom.

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

Limited Magic Immunity. Unless he wishes to be affected, Abzu is immune to spells of 5th level or lower. He has advantage on saving throws against all other spells and magical effects.

Magic Weapons. Abzu’s weapon attacks are magical.

Multiple Heads. Abzu can take one reaction per turn, rather than only one per round. He also has advantage on saving throws against being knocked unconscious. If he fails a saving throw against an effect that would stun a creature, one of his unspent legendary actions is spent.

Regeneration. If Abzu has at least 1 hit point, he regains 30 hit points at the start of his turn.

Multiattack. Abzu can use his Frightful Presence. He then makes three attacks: two with his claws and one with his tail.

Claw. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 24 (4d6 + 12) slashing damage.

Tail. Melee Weapon Attack: +17 to hit, reach 25 ft., one target. Hit: 28 (4d8 + 12) piercing damage.

Frightful Presence. Each creature of Abzu’s choice that is within 240 feet of Abzu and aware of him must succeed on a DC 24 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to Abzu’s Frightful Presence for the next 24 hours.

Abzu 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. Abzu regains spent legendary actions at the start of his turn.

Abzu’s legendary action options are associated with his five dragon heads (a bite and a breath weapon for each). Once Abzu chooses a legendary action option for one of his heads, he can’t choose another one associated with that head until the start of his next turn.

Bite. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 34 (4d10 + 12) slashing damage plus 14 (4d6) necrotic damage (shadow dragon head), force damage (arcane dragon head), thunder damage (storm dragon head), radiant damage (yellow dragon head), or psychic damage (black-green dragon head).

Shadow Dragon Head: Necrotic Breath (Costs 2 Actions). Abzu breathes a necrotic shadow in a 120-foot line that is 10 feet wide. Each creature in that line must make a DC 25 Dexterity saving throw, taking 69 (15d8) necrotic damage on a failed save, or half as much damage on a successful one. A failed creature cannot be healed until the end of the Abzu's next turn.

Yellow Dragon Head: Radiant Breath (Costs 2 Actions). Abzu breathes radiant light in a 120-foot line that is 10 feet wide. Each creature in that line must make a DC 23 Dexterity saving throw, taking 90 (16d10) radiant damage on a failed save, or half as much damage on a successful one. A failed creature emits a bright light in a 10 foot radius, even if she is invisible.

Black-Green Dragon Head: Psychic Breath (Costs 2 Actions). Abzu unleashes a psychic wave in a 90-foot cone. Each creature in that area must make a DC 25 Constitution saving throw, taking 79 (22d6) psychic damage on a failed save, or half as much damage on a successful one. A failed creature has disadvantage on the next weapon or spell attack she takes.

Storm Dragon Head: Thunder Breath (Costs 2 Actions). Abzu lets out a wave of thunder in a 90-foot cone. Each creature in that area must make a DC 23 Dexterity saving throw, taking 93 (26d6) thunder damage on a failed save, or half as much damage on a successful one. A failed creature also falls prone.

Arcane Dragon Head: Force Breath (Costs 2 Actions). Abzu breathes a blast of force in a 90-foot cone. Each creature in that area must make a DC 25 Dexterity saving throw, taking 74 (16d8) force damage on a failed save, or half as much damage on a successful one. A failed creature is also pushed 10 feet away from Abzu.