Ancient Blue Dragon
Gargantuan Dragon, Lawful Evil
AC 22
HP 481 ()
Speed 40 ft., Burrow 40 ft., Fly 80 ft.
Saving Throws DEX , WIS
Skills Perception , Stealth
Immunities Lightning
Senses Darkvision 120 ft., Blindsight 60 ft., Passive Perception 27
Languages Common, Draconic
CR 23 (XP 50,000; PB +7)
Traits
Legendary Resistance (4/Day, or 5/Day in Lair). If the dragon fails a saving throw, it can choose to succeed instead.
Actions
Multiattack. The dragon makes three Rend attacks. It can replace one attack with a use of Spellcasting to cast Shatter (level 3 version).
Rend. Melee Attack Roll: , reach 15 ft. Hit: 18 () Slashing damage plus 11 () Lightning damage.
Lightning Breath (Recharge 5–6). Dexterity Saving Throw: DC 23, each creature in a 120-foot-long, 10-foot-wide Line. Failure: 88 () Lightning damage. Success: Half damage.
Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 22):
Legendary Actions
Cloaked Flight. The dragon uses Spellcasting to cast Invisibility on itself, and it can fly up to half its Fly Speed. The dragon can’t take this action again until the start of its next turn.
Sonic Boom. The dragon uses Spellcasting to cast Shatter (level 3 version). The dragon can’t take this action again until the start of its next turn.
Tail Swipe. The dragon makes one Rend attack.