Gargantuan dragon, chaotic evil

Armor Class 22 (natural armor)
Hit Points 546 (28d20 + 252)
Speed 40 ft., climb 40 ft., fly 80 ft.

STR	DEX	CON	INT	WIS	CHA
30 (+10)	10 (+0)	29 (+9)	18 (+4)	15 (+2)	23 (+6)

Saving Throws Dex +7, Con +16, Wis +9, Cha +13
Skills Perception +16, Stealth +7
Damage Resistances 
Damage Immunities fire
Condition Immunities 
Senses blindsight 60 ft., darkvision 120 ft., passive Perception 26
Languages Common, Draconic
Challenge 24 (62000 XP)

Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Actions

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) piercing damage plus 14 (4d6) fire damage.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 17 (2d6 + 10) slashing damage.

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) 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 24 Dexterity saving throw, taking 91 (26d6) fire damage on a failed save, or half as much damage on a successful one.

Legendary Actions

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.

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.