Ancient Blue Dragon

3/day. If the ancient blue 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 blue dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Melee Weapon Attack: +16 to hit, reach 15 ft.. Hit: 20 (2d10 + 9) piercing plus 11 (2d10) lightning damage.

Melee Weapon Attack: +16 to hit, reach 10 ft.. Hit: 16 (2d6 + 9) slashing damage.

Melee Weapon Attack: +16 to hit, reach 20 ft.. Hit: 18 (2d8 + 9) bludgeoning damage.

Recharge 5–6. The dragon exhales lightning in a 120-foot line (5 ft. wide). Each creature in that line must make a DC 23 Dexterity saving throw, taking 88 (16d10) lightning damage on a failed save, or half as much damage on a successful one.

Each creature of the ancient blue dragon's choice that is within 120 ft. of the dragon and aware of it must succeed on a DC 20 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 blue dragon's Frightful Presence for the next 24 hours.

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

The ancient blue dragon makes a tail attack.

Costs 2 legendary actions. The ancient blue dragon beats its wings. Each creature within 15 ft. of the ancient blue dragon must succeed on a DC 24 Dexterity saving throw or take 16 (2d6 + 9) bludgeoning damage and be knocked prone. The ancient blue dragon can then fly up to half its flying speed.