Undead Blue Dragon

Legendary Resistance (2/Day). If the dragon fails a saving throw, it can choose to succeed instead.

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

Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 13 (1d10 + 7) piercing damage plus 5 (1d10) necrotic damage.

Claw. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 11 (1d6 + 7) slashing damage.

Tail. Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 12 (1d8 + 7) 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 15 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.

Lightning Breath (Recharge 5–6). The dragon exhales lightning in a 90-­foot line that is 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw, taking 18 (3d10) lightning damage on a failed save, or half as much damage on a successful one.