Ancient Blue Dragon
Gargantuan dragon, lawful evil
STR
29
DEX
10
CON
27
INT
18
WIS
17
CHA
21
Armor Class: 22
Hit Points: 481 (26d20+208)
Speed: Walk 40 ft., Swim
Challenge Rating: 23 (50000 XP)
Saving Throws: Dex +7 Con +15 Wis +10 Cha +12
Skills: Perception +17 Stealth +7
Senses: blindsight 60 ft. darkvision 120 ft. passive perception 27
Languages: Common, Draconic
Legendary Resistance
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: +16 to hit, reach 15 ft., one target. Hit: 20 (2d10 + 9) piercing damage plus 11 (2d10) lightning damage.
Claw
Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 16 (2d6 + 9) slashing damage.
Tail
Melee Weapon Attack: +16 to hit, reach 20 ft., one target. Hit: 18 (2d8 + 9) 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 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 dragon's Frightful Presence for the next 24 hours.
Lightning Breath
The dragon exhales lightning in a 120-foot line that is 10 feet 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.
Legendary Actions
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 ft. of the dragon must succeed on a DC 24 Dexterity saving throw or take 16 (2d6 + 9) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.