Legendary Resistance (3/Day). if Andavariel fails a saving throw, she can choose to succeed instead.
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 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. 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.
Andavariel can make 1 action per turn. Multiattack or Breath Weapon. Her Frightful Presence aura activates at the start of each turn when desired.
Multiattack. The dragon makes three attacks: one with its bite and two with its claws.
Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage.
Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.
Tail. Melee Weapon Attack: +7 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage.
Breath Weapons (Recharge 5–6). Andavariel uses the following breath weapon.
Cold Breath. The dragon exhales an icy blast in a 30-foot cone. Each creature in that area must make a DC 17 Constitution saving throw, taking 54 (12d8) cold damage on a failed save, or half as much damage on a successful one.
Andavariel 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. She regains spent legendary actions at the start of her turn.
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.
Lair and Lair Actions
Andavariel’s Lair
Spending thousands of years within her prison Andavariel's influence has spread into every crack in the stone as she has slowly oozed her power through the dungeon. This has given her an immense amount of magical power which she can tap into at any time she wishes.
Lair Actions
On initiative count 20 (losing initiative ties), the dragon takes a lair action to cause one of the following effects:
Ice Storm (DC 17). Each creature in a 20-foot-radius, 40-foot-high cylinder must make a Dexterity save. A creature takes 2d8 bludgeoning and 4d6 cold damage on a failed save, or half on a success. Additionally, the area is difficult terrain until the end of your next turn.
Sleet Storm (5 rounds, DC 17). A 20-foot-tall, 40-foot radius cylinder centered on a point you choose is heavily obscured by thick sleet. Exposed flames in the area are doused. The ground becomes difficult terrain. When a creature enters the area for the first time or starts its turn there, it must make a Dexterity save. On a failure, it falls prone. If a creature is concentrating, it must make a Constitution save to maintain it.