Flyby. Arendagrost doesn't provoke an opportunity attack when he flies out of an enemy's reach.
Grappler. Arendagrost has advantage on attack rolls against any creature grappled by him.
Inhibitor Release (Mythic Trait; Recharges after a Short or Long Rest). If Arendagrost is reduced to 0 hit points, he doesn't die or fall unconscious. Instead, he regains 750 hit points. In addition, he gains the benefits of the primordial ward spell for one hour (resistance to cold, force, necrotic, psychic, and thunder damage instead of acid, cold, fire, lightning, and thunder), without requiring concentration. Finally, the area affected by his Profane Devastation acts as an antimagic field for one hour.
Legendary Resistance (3/Day). If Arendagrost fails a saving throw, he can choose to succeed instead.
Magic Resistance. Arendagrost has advantage on saving throws against spells and other magical effects. Additionally, he is immune to any trait that would multiply damage against him.
Magic Weapons. Arendagrost’s weapon attacks are magical.
Overwhelming Strength (Inhibitor Release only). When Arendagrost hits with a melee attack, he can also push the target up to 10 feet away from him if the target is no more than two sizes larger than it.
Regeneration. If Arendagrost has at least 1 hit point, he regains 20 hit points at the start of his turn.
Siege Monster. Arendagrost deals double damage to objects and structures.
Three Heads. Arendagrost has advantage on saving throws against being blinded, deafened, stunned, and knocked unconscious.
Multiattack. Arendagrost makes four tentacle attacks.
Tentacle. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 49 (6d12 + 10) bludgeoning damage.
Mystic Eyes of Death. Arendagrost turns his magical gaze toward one non-celestial creature that he can see within 30 feet of him. The target must make a DC 27 Constitution saving throw or drop to 0 hit points. If the saving throw fails by 5 or more, the target also falls unconscious. Unless the target is incapacitated, it can avert its eyes to avoid the gaze and to automatically succeed on the save. If the target does so, it can’t see Arendagrost until the start of his next turn. If the target looks at him in the meantime, it must immediately make the save.
Profane Devastation (Recharges after 1 minute). Arendagrost emits a massive explosion of negative energy, wreaking havoc in a 150-foot radius sphere centered on himself. Each hostile creature in that area must make a DC 27 Dexterity saving throw. On a failed save, a creature takes 91 (26d6) necrotic damage and is deafened. A creature deafened in this way is paralyzed. On a successful save, a creature takes half as much damage and isn't deafened. A deafened creature can repeat its saving throw at the end of each of its turns, ending the effect on itself on a success.
In addition, unsecured nonmagical objects that are completely within the sphere also take damage. Also, the spell emits bright light in a 1500-foot-sphere radius centered on Arendagrost until the end of his turn and emits a thunderous boom audible out to 2 miles.
Shrug It Off (Inhibitor Release only). Arendagrost halves the damage he takes from an attack. He must be able to see the attacker.
Arendagrost can take 3 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. Arendagrost regains spent legendary actions at the start of his turn.
Bite. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 32 (4d10 + 10) slashing damage plus 14 (4d6) acid damage (central head), cold damage (right head), or fire damage (left head). If the attack is a critical hit, then the target is grappled (escape DC 27).
Right Head: Cold Breath (Costs 2 Actions). Arendagrost breathes an icy blast in a 50-foot cone. Each creature in that area must make a DC 27 Dexterity saving throw, taking 70 (20d6) cold damage on a failed save, or half as much damage on a successful one.
Central Head: Acid Breath (Costs 2 Actions). Arendagrost breathes acid in a 100-foot line that is 10 feet wide. Each creature in that line must make a DC 27 Dexterity saving throw, taking 70 (20d6) acid damage on a failed save, or half as much damage on a successful one.
Left Head: Fire Breath (Costs 2 Actions). Arendagrost breathes fire in a 50-foot cone. Each creature in that area must make a DC 27 Dexterity saving throw, taking 70 (20d6) fire damage on a failed save, or half as much damage on a successful one.
If Arendagrost’s mythic trait is active, he can use the options below as legendary actions for 1 hour after using Inhibitor Release.
Wrath of the Abyssal Maw (Costs 3 actions). Arendagrost ends all magic around him with his sheer will. He casts dispel magic, targeting any number of creatures or magical effects he can see within 120 feet and ignoring immunity to the dispel magic spell.
Description
Maw of The Abyss. Known as the Maw of the Abyss, Arendagrost is a fearsome denizen of the Abyss. He is the most powerful of the hideous spawn of Demogorgon, the Prince of Demons and Malcanthet, Queen of Succubi and one of the eldest of the seven children the 2 have sired. Arendagrost is described as vaguely resembling an immense wingless dragon of gargantuan size. Instead of legs, it moves upon a sea of tentacles. In place of scales, it is covered in coarse black fur and has three heads that resemble monstrous horned fiends that breath bloody acid, fire, and frost. Its six-fold eyes offer instant death to anyone catching their hideous gaze.
Horror of Horrors. Arendagrost is the most powerful of the hideous spawn of Demogorgon and Malcanthet, and even his father finds him unsettling to look upon. But do to the results of his rampage during the part of the profaned ritual performed by Lord Kargoth, first of the death knights, that saw Arendagrost released from it's prison, he proved his worth to his father, Demogorgon seeing that Arendagrost could be used to enforced his will if monitored carefully. The prince of demons created a lair for Arendagrost beneath the Fortress of Ungorth Reddik, where it could serve to guard the land approach to his capital city of Lemoriax. Arendagrost also proved to be an expedient way to dispose of powerful prisoners that Demogorgon wished to eliminate.
Tarrasque of the Great Wheel. After Arendagrost's hundred year long banishment that followed his defeat, Demogorgon began to use it more cautiously to wreak havoc and destruction on other layers of the abyss and other planes. Legends tell of a small material plane world, no cold and dead, that incurred the Demogorgon's wrath. He sent Arendagrost to punish it for a century. In addition both Orcus and Graz'zt have felt the heavy tread of the Maw of the Abyss in assaults upon their homes. In addition to it's first death upon the material plane, Arendagrost has been slain twice in combat with Orcus, though always at the cost of many of the Prince of Undeath's most powerful servants, banishing it again to the Gaping Maw. As Arendagrost once again nears the end of it's latest banishment Demogorgon has been contemplating new strategies of deployment against powerful strongholds on the material plane rather than wasting it's might in futile battles with other demon lords. In a few short years, the "Tarrasque of the Great Wheel" will once again prey upon the mortal worlds.
Pure Hatred, Cruelty, and Destruction. Arendagrost is a being of pure hate, and tends to crash into combat in almost mindless savagery, reveling in the destruction it causes. Creatures slain or incapacitated are devoured as soon as possible. The destruction caused by it's three draconic heads is of particular amusement to the creature, and it attacks with it's breath weapons as often as possible, delighting in turning it's ire onto creatures who are near death, waiting for them to beg for mercy or quivering in terror before obliterating them. Arendagrost only withdraws from combat at Demogorgon's direct order.