Ossalith, Heartbone Dragon

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Gargantuan Dragon (bone, ancient, bone-shroud), Lawful Evil

Armor Class 20 (natural armor)

Hit Points 348 (24d20+96)

Speed 40 ft. fly 60 ft.

STR 26 (+8)

DEX 14 (+2)

CON 18 (+4)

INT 16 (+3)

WIS 14 (+2)

CHA 22 (+6)

Saving Throws Dex +7, Con +9, Wis +7

Skills Perception +7

Damage Resistances necrotic

Damage Immunities necrotic

Senses darkvision 120 ft., passive Perception 17

Languages Common, Draconic, Ancient

Challenge 16 (15,000 XP) Proficiency Bonus +5

Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Keen Senses. The dragon has advantage on Wisdom (Perception) checks relying on sight, hearing, or smell.

Magic Resistance. The dragon has advantage on saving throws against spells and other magical effects.

Floating Bone Orbit. A halo of bone shards floats around the dragon's living heart. The orbiting bones grant the dragon a +2 bonus to AC and to saving throws.

Actions

Multiattack. The dragon makes two claw attacks and one bite attack.

Bite. Melee weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 21 (2d12+8) piercing damage.

Claw. Melee weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 17 (2d8+8) slashing damage.

Legendary Actions

The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. The dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Bone Volley. The dragon hurls bone fragments at a target within 60 feet. The dragon makes a ranged attack roll.

Bone Storm (Costs 2 Actions). The floating bones around Ossalith surge outward in a 20-foot radius. Each creature in the area must succeed on a DC 18 Dexterity saving throw or take 3d6 slashing damage, or half on a successful save.

Environment Underdark, Mountain

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Lore & Description

Appearance

An ancient dragon whose bones float around its still-living heart. Its mass is wrapped in ivory and marrow, a living furnace-glow beating at the center of its chest. Thousands of bone shards whirl around that heart, forming a shifting lattice that both armor-pads its hide and lashes out when provoked. The bone halo can detach to lash at intruders, then reassemble as the dragon bleeds and breathes, as if the lattice itself feeds on its own life to stay intact.

Behavior & Origins

Ossalith, the Heartbone Dragon, is a relic of an age when dragons learned to bind bone to blood and marrow to magic. The halo of floating bones began as a macabre ritual to protect a dragon's heart from puncture and theft; over centuries, the lattice grew sentience of its own, whispering old oaths and warnings. Ossalith uses its bone shards to trap, distract, and dismember foes, turning the battlefield into a shifting cathedral of bone. Legends tell that severing the heart's tether to the bone lattice might shatter the dragon's defense, but at a tremendous cost—cataclysmic necrotic energy may ripple through the world if the lattice collapses.

Generation Info

Original prompt:
"An ancient dragon whose bones float around its still-living heart."

Created: Feb 2, 2026
Modified: May 22, 2026