Ancient Black Dragon

Gargantuan Dragon (Chromatic), Chaotic Evil

AC: 22

Initiative: +16 (26)

HP: 367 (21d20 + 147)

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

STR
27 (+8)
DEX
14 (+2)
CON
25 (+7)
INT
16 (+3)
WIS
15 (+2)
CHA
22 (+6)

Saving Throws: Dex +9, Wis +9

Skills: Perception +16, Stealth +9

Immunities: acid

Senses: Blindsight 60 ft., Darkvision 120 ft., Passive Perception 26

Languages: Common, Draconic

CR: 21 (XP 33,000, or 41,000 in lair; PB +7)

Habitat: Swamp

Treasure: Relics

Amphibious.

The dragon can breathe air and water.

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 21, +13 to hit with spell attacks):

At will: Detect Magic, Fear, Melf's Acid Arrow (level 4 version)

1/day each: Create Undead, Speak with Dead, Vitriolic Sphere (level 5 version)

Actions

Multiattack.

The dragon makes three Rend attacks. It can replace one attack with a use of Spellcasting to cast Melf's Acid Arrow (level 4 version).

Rend.

Melee Attack Roll: +15, reach 15 ft. Hit: 17 (2d8 + 8) Slashing damage plus 9 (2d8) Acid damage.

Acid Breath (Recharge 5-6).

Dexterity Saving Throw: DC 22, each creature in a 90-foot-long, 10-foot-wide Line. Failure: 67 (15d8) Acid 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.

Cloud of Insects.

Dexterity Saving Throw: DC 21, one creature the dragon can see within 120 feet. Failure: 33 (6d10) Poison damage, and the target has Disadvantage on saving throws to maintain Concentration until the end of its next turn. Failure or Success: The dragon can't take this action again until the start of its next turn.

Frightful Presence.

The dragon uses Spellcasting to cast Fear. The dragon can't take this action again until the start of its next turn.

Pounce.

The dragon moves up to half its Speed, and it makes one Rend attack.

Regional Effects

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

  • Acrid Haze.

    Odorous and stifling fog covers the area within 1 mile of the lair, rendering that area Lightly Obscured. Travel for creatures other than the dragon and its allies takes twice the usual time in that area.

  • Foul Water.

    Water sources within 1 mile of the lair are supernaturally fouled. A creature that drinks such water must succeed on a DC 15 Constitution saving throw or have the Poisoned condition for 1 hour.

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

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Ancient Black Dragon

Source: Monster Manual (2025), p. 40 - Licenses and attribution