Ancient Blue Dragon
Gargantuan Dragon (chromatic), Lawful EvilAC 22
HP 481 (26d20 + 208)
Speed 40 ft., burrow 40 ft., fly 80 ft.
STR
29 (+9)
Save +9
DEX
10 (+0)
Save +7
CON
27 (+8)
Save +8
INT
18 (+4)
Save +4
WIS
17 (+3)
Save +10
CHA
25 (+7)
Save +7
Saving Throws DEX +7, WIS +10
Skills Perception +17, Stealth +7
Immunities Lightning
Senses Blindsight 60 ft., Darkvision 120 ft., Passive Perception 27
Languages Common, Draconic
CR 23
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: +16, reach 15 ft. Hit: 18 (2d8 + 9) Slashing damage plus 11 (2d10) Lightning damage.
Lightning Breath (Recharge 5+). dex 23, each creature in a 120-foot-long, 10-foot-wide Line. Failure: 88 (16d10) Lightning damage. Success: Half damage.
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.