Ancient White Dragon

3/day. If the ancient white dragon fails a saving throw, it can choose to succeed instead.

3 legendary actions; one at a time at the end of another creature’s turn, regaining spent uses at the start of its turn

The ancient white dragon can move across and climb icy surfaces without needing to make an ability check. Additionally, difficult terrain composed of ice or snow doesn't cost it extra movement.

Melee Weapon Attack: +14 to hit, reach 15 ft.. Hit: 19 (2d10 + 8) piercing plus 9 (2d8) cold damage.

Melee Weapon Attack: +14 to hit, reach 10 ft.. Hit: 15 (2d6 + 8) slashing damage.

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

Each creature of the ancient white dragon's choice that is within 120 ft. of the dragon and aware of it must succeed on a DC 16 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 ancient white dragon's Frightful Presence for the next 24 hours.

Melee Weapon Attack: +14 to hit, reach 20 ft.. Hit: 17 (2d8 + 8) bludgeoning damage.

Recharge 5–6. The ancient white dragon exhales an icy blast of hail in a 90-foot cone. Each creature in that area must make a DC 22 Constitution saving throw, taking 72 (16d8) cold damage on a failed save, or half as much damage on a successful one.

The ancient white dragon makes a Wisdom (Perception) check.

The ancient white dragon makes a tail attack.

Costs 2 legendary actions. The ancient white dragon beats its wings. Each creature within 15 ft. of the ancient white dragon must succeed on a DC 22 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The ancient white dragon can then fly up to half its flying speed.