Death Throes. When the dragon dies, it explodes, and each creature within 30 feet of it must make a DC 19 Dexterity saving throw, taking 86 (20d6+16) magical fire damage on a failed save, or half as much on a successful one. The explosion doesn't ignite flammable objects. Fire Aura. At the start of each of the dragon's turns, each creature within 10 feet of it takes 18 (3d6+8) fire damage, and flammable objects in the aura that aren't being worn or carried ignite. A creature that touches the dragon or hits it with a melee attack within 5 feet of it takes 18 (3d6+8) fire damage. Magical Resistance. The dragon has advantage on saving throws against spells and other magical effects. Magic Weapons. The dragon's bite, claw and tail attacks are magical. Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead. Everlasting Persistence. If the dragon kills a creature level/ CR 15 or above, the dragon regains a used Legendary Resistance. Draconic & Demonic strength. The dragon has advantage on strength checks and saving throws.
Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws or the dragon then makes three attacks: one with its bite, one with its claw and one with its tail. Bite. Melee Weapon Attack: +20 to hit, reach 15 ft., one target. Hit: 23 (2d10 + 12) piercing damage plus 14 (4d6) fire damage. Claw. Melee Weapon Attack: +20 to hit, reach 10 ft., one target. Hit: 19 (2d6 + 12) slashing damage. Tail. Melee Weapon Attack: +20 to hit, reach 20 ft., one target. Hit: 21 (2d8 + 12) bludgeoning damage. Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 21 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 the dragon's Frightful Presence for the next 24 hours. Fire Breath (Recharge 5–6). The dragon exhales fire in a 90-foot cone. Each creature in that area must make a DC 25 Dexterity saving throw, taking 91 (26d6) fire damage on a failed save, or half as much damage on a successful one. Demon's Essense Fire Breath (Recharge 5-6). The dragon exhales smoke with crackling crackling embers that explode with fire on contact in a 40-foot cone. Each creature in that area must make a DC 23 Dexterity saving throw, taking 76 (15d8) fire damage on a failed save, or half as much damage on a successful one. Demonic Dragon's Cry (Only usable after the dragon makes two breath attacks). The dragon yells a mighty roar and then lower his mouth as he exhales fire and black smoke with crackling embers inside the smoke in a 90-foot cone, except, time cracks as he does. Each creature in that area must make a DC 21 Dexterity save with disadvantage, taking (27d10+6) on a failed save, or no damage on a successful one. The dragon's breath attacks aside from this one are no longer recharging. Teleport. The dragon magically teleports, along with any equipment or creature it is wearing or carrying, up to 120 feet to an unoccupied space it can see.
The dragon 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. The dragon regains spent legendary actions at the start of its turn. Detect. The dragon makes a Wisdom (Perception) check. Tail Attack. The dragon makes a tail attack. Teleport (Costs 2 Actions). The dragon uses it's teleport. Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.
On initiative count 20 (losing initiative ties), the dragon takes a lair action to cause one of the following effects; the dragon can’t use the same effect two rounds in a row:
The region containing a legendary red dragon’s lair is warped by the dragon’s magic, which creates all of the following effects:
The odour of sulphur and pumice surrounds a red dragon, whose swept-back horns and spinal frill define its silhouette. Its beaked snout vents smoke at all times, and its eyes dance with flame when it is angry. An extremely old red dragon, Ashardalon had an appearance that diverged somewhat from usual ancient dragons of his kind. He possessed unusual demonic features and a scar on his chest in the shape of a balor.
Mountains, Astral Plane