Ancient Blue Dragon

Gargantuan Dragon (Chromatic), Lawful Evil

AC: 22

Initiative: +14 (24)

HP: 481 (26d20 + 208)

Speed: 40 ft., burrow 40 ft., fly 80 ft.

STR
29 (+9)
DEX
10 (+0)
CON
27 (+8)
INT
18 (+4)
WIS
17 (+3)
CHA
25 (+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 (XP 50,000, or 62,000 in lair; PB +7)

Habitat: Coastal, Desert

Treasure: Relics

Legendary Resistance (4/Day, or 5/Day in Lair).

If the dragon fails a saving throw, it can choose to succeed instead.

Spellcasting.

The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 22):

At will: Detect Magic, Invisibility, Mage Hand, Shatter (level 3 version)

1/day each: Scrying, Sending

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 5-6).

Dexterity Saving Throw: DC 23, each creature in a 120-foot-long, 10-foot-wide Line. Failure: 88 (16d10) Lightning damage. Success: Half damage.

Legendary Actions

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature's turn, this creature can expend a use to take one of the following actions; it regains all expended uses at the start of each of its turns.

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.

Regional Effects

The region containing an adult or ancient blue dragon's lair is changed by its presence, creating the following effects:

  • Sinkholes.

    Sinkholes form more frequently in the area within 1 mile of the lair. Whenever a creature in that area other than the dragon and its allies finishes a Long Rest, roll 1d20. On a 1, a sinkhole opens beneath the creature, and the creature must succeed on a DC 15 Dexterity saving throw or fall 2d4 × 10 feet into the sinkhole.

  • Spiteful Storms.

    Dust devils and thunderstorms rage within 1 mile of the lair. The area is Lightly Obscured.

If the dragon dies or moves its lair elsewhere, these effects end immediately.

Find this creature in the encounter builder

Ancient Blue Dragon

Source: Monster Manual (2025), p. 50 - Licenses and attribution