Amphibious. Abbathor can breathe air and water.

Aura of Decaying Greed. Any creature that starts its turn within 15 feet of Abbathor must succeed on a DC 17 Constitution saving throw or take 2d6 necrotic damage, and they cannot regain hit points until the start of their next turn.

Curse of the Hoarder's Blood. As a bonus action, Abbathor can target one creature he can see within 60 feet carrying non-magical treasure. The creature must succeed on a DC 17 Wisdom saving throw or drop its most valuable non-magical treasure. Until the start of the creature's next turn, any of Abbathor's attacks that hit the creature deal an extra 1d8 poison damage.

Curse Synergy. A creature cannot be affected by more than one instance of the "disadvantage on all attack rolls" curse (Lair Effect or Corrosive Curse) at the same time. However, a creature affected by that curse CAN also be affected by the Impose Ill-Fortune Legendary Action.

Legendary Resistance (3/Day, 4/Day in Lair). If Abbathor fails a saving throw, he can choose to succeed instead.

The Price of Avarice. Abbathor has advantage on attack rolls against any creature carrying at least 500 gp of non-magical treasure. Furthermore, any creature that casts a spell requiring a material component worth 50 gp or more within 60 feet of Abbathor has disadvantage on the spell's attack roll or saving throw DC.

Actions

Multiattack. Abbathor can make three melee attacks. He can replace up to two attacks with a use of Spellcasting to cast Circle of Death (7th level version).

Smash (Great Axe). Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 20 (2d8+11) Slashing damage plus 7 (2d6) Acid damage.

Acid Breath (Recharge 5–6). Abbathor exhales acid in an 80-foot line that is 10 feet wide. Each creature in that line must make a DC 20 Dexterity saving throw, taking 54 (12d8) acid damage on a failed save, or half as much damage on a successful one.

Blight of Avarice. Melee Spell Attack: +13 to hit, reach 10 ft., one target. Hit: 9 (2d8) necrotic damage, and the target must succeed on a DC 17 Wisdom saving throw or drop one non-magical item it is holding.

Spellcasting. Abbathor casts one of the following spells (spell save DC 17):

• At Will: Fear, Circle of Death (3rd level)
• 3/Day: Counter spell, curse of see no evil, speak no evil, and hear no evil.
• 1/Day Each: Bestow Curse, Eyebite, Vitriolic Sphere

Curse of the Hoarder's Blood. As a bonus action, Abbathor can target one creature he can see within 60 feet carrying non-magical treasure. The creature must succeed on a DC 17 Wisdom saving throw or drop its most valuable non-magical treasure. Until the start of the creature's next turn, any of Abbathor's attacks that hit the creature deal an extra 1d8 poison damage.

Toxic Adaptation. As a bonus action, Abbathor can choose one creature within 30 feet that is currently Poisoned or Cursed. That creature has disadvantage on its next saving throw against a spell or ability cast by Abbathor before the end of its next turn.

Acidic Burst. As a bonus action, Abbathor causes a splash of caustic ooze to strike one target he can see within 15 feet. The target must succeed on a DC 17 Dexterity saving throw or take 1d10 acid damage. If the target is wearing non-magical armor or is holding a non-magical shield, it takes an additional 1d4 damage, and the item is pitted and takes a permanent and cumulative -1 penalty to the AC it grants. If its penalty drops to -5, the item is destroyed.

Blade of Disaster. You create a blade-shaped planar rift about 3 feet long in an unoccupied space you can see within range. The blade lasts for the duration. When you cast this spell, you can make up to two melee spell attacks with the blade, each one against a creature, loose object, or structure within 5 feet of the blade. On a hit, the target takes 4d12 force damage. This attack scores a critical hit if the number on the d20 is 18 or higher. On a critical hit, the blade deals an extra 8d12 force damage (for a total of 12d12 force damage).

Acidic Burst. As a bonus action, Abbathor causes a splash of caustic ooze to strike one target he can see within 15 feet. The target must succeed on a DC 17 Dexterity saving throw or take 1d10 acid damage. If the target is wearing non-magical armor or is holding a non-magical shield, it takes an additional 1d4 damage, and the item is pitted and takes a permanent and cumulative -1 penalty to the AC it grants. If its penalty drops to -5, the item is destroyed.

Jealous Retaliation. When a creature Abbathor can see within 60 feet casts a spell or uses an item that expends a charge/slot, Abbathor can use his reaction to force the creature to make a DC 18 Wisdom saving throw. On a failure, the spell slot/charge is wasted, and the creature suffers one level of Exhaustion.

Venomous Parry. When a creature hits Abbathor with a melee attack, Abbathor can use his reaction to force the attacker to make a DC 18 Constitution saving throw. On a failure, the creature takes 14 (4d6) poison damage and becomes Poisoned until the end of its next turn.

Legendary Actions

Abbathor can take 3 Legendary Actions (4 in his Lair).

• Smash. Abbathor moves up to half his speed and makes one Smash attack.
• Pustulent Spores. Abbathor exhales spores in a 20-ft. cube. Each creature in that area must make a DC 17 Constitution save, taking 10 (3d6) poison damage on a failed save. If a creature that fails this save is also cursed or poisoned, it takes an additional 4 (1d8) necrotic damage, and Abbathor regains hit points equal to the necrotic damage dealt.
• Grasping Head of Corrosion (Costs 2 Actions). Abbathor makes two separate attacks against two different creatures, choosing from: Smash, Blight of Avarice, or Spellcasting (Circle of Death, 3rd level).
• Impose Ill-Fortune (Costs 3 Actions). Abbathor targets one creature, which must succeed on a DC 17 Wisdom saving throw or be cursed with ill-fortune until the end of its next turn. While cursed, the creature must subtract 1d4 from all attack rolls, saving throws, and ability checks it makes.

Abbathor (Mythic Draconic Form)

When Abbathor drops to 0 hit points, his body erupts in a torrent of acid and poisonous fumes. He is not slain but undergoes a mythic transformation. He regains all his Legendary Resistances and can't take damage till the start of his next turn also he immediately takes a Mythic Action . His stat block changes as follows:

Size Huge Draconic (Titan)

Armor Class 25 (Natural Armor)

Hit Points 450 (New Maximum)

Speed 40 ft., swim 40 ft., fly 80 ft.

Mythic Aura of Decaying Greed. Abbathor's aura intensifies. Its range increases to 30 feet and its damage increases to 14 (4d6) necrotic damage.

Magic Resistance. Abbathor has advantage on saving throws against spells and other magical effects.

Caustic Body. A creature that touches Abbathor or hits him with a melee attack while within 5 feet of him takes 11 (2d10) acid damage.

Draconic Frightful Presence. Each creature of Abbathor's choice that is within 120 feet of him and aware of him must succeed on a DC 18 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.

Mythic Actions

On initiative count 20 (losing ties), Abbathor can take one of the following Mythic Actions (he can no longer take Lair Actions):

• Corrosive Curse. Abbathor creates a corrosive wave in a 30-ft. radius. Each creature must make a DC 20 Dexterity save. On a failure, a creature takes 21 (6d6) acid damage plus 21 (6d6) necrotic damage and is Cursed with disadvantage on all attack rolls for 1 minute.
• Essence of Acid. When a creature hits Abbathor, it takes 27 (6d8) acid damage and is Restrained (escape DC 20 Constitution save).
• Spirit of Poison. Abbathor creates a 120-ft. sphere of poison. Creatures in the sphere take 54 (12d8) poison damage and are Poisoned. Abbathor becomes Invisible. Until the end of Abbathor's next turn, enemies have disadvantage on all saving throws against his spells and abilities.

Actions

Multiattack. Abbathor makes four attacks: two with his Empowered Smash and two with his Tail.

Empowered Smash. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 23 (2d12+10) slashing damage plus 14 (4d6) acid damage.

Tail. Melee Weapon Attack: +16 to hit, reach 20 ft., one target. Hit: 24 (3d8+10) bludgeoning damage, and the target must succeed on a DC 20 Strength saving throw or be knocked prone.

(Abbathor retains his Acid Breath and Spellcasting actions.)

Mythic Legendary Actions

Abbathor has 4 Legendary Actions. He can no longer use his previous Legendary Actions, and instead chooses from the options below.

• Tail Sweep (Costs 1 Action). Abbathor sweeps his tail. Each creature in a 20-foot cone must succeed on a DC 20 Dexterity saving throw or take 17 (2d6+10) bludgeoning damage and be knocked prone.
• Corrosive Bile (Costs 1 Action). Abbathor spits a glob of acid at one target he can see within 60 feet. The target must make a DC 20 Dexterity saving throw, taking 27 (6d8) acid damage on a failed save, or half as much on a success.
• Wing Attack (Costs 2 Actions). Abbathor beats his wings. Each creature within 15 feet of him must succeed on a DC 22 Dexterity saving throw or take 17 (2d6+10) bludgeoning damage and be knocked prone. Abbathor can then fly up to half his flying speed.