Actions

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.   Bite. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: (3d10 + 10) piercing.   Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: (3d6 + 10) slashing damage.   Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: (3d8 + 10) bludgeoning damage. If the target is a creature, it must make a DC 25 (8 +Prof + Str) Strength saving throw or be knocked prone   Frightful Presence. Each creature of the dragon's choice that is within 120 ft. of the dragon and aware of it must succeed on a DC 19 (8 + Prof + Cha) Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.   Blade Breath (Recharge 5-6). The dragon exhales a stream of adamantine blades in a 120-foot line that is 10 feet wide. Each creature in that area must make a DC 25 (8 + Prof + Str) Dexterity saving throw, taking 66 (12d10) slashing damage on a failed save, or half as much damage on a successful one. Any object or structure in the area takes 132 (24d10) slashing damage. In either case this damage counts as having come from an adamantine weapon for the proposes of overcoming resistances.

Legendary Actions

The Ancient Adamantine Dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The Ancient Adamantine Dragon regains spent legendary actions at the start of their turn.   Detect. The dragon makes a Wisdom (Perception) check.   Tail Attack. The dragon makes a tail attack.   Bulwark. The dragon gains resistance to a damage type of it's choice until the end of it's next turn.   Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 5 ft. of the dragon must succeed on a DC 25 Dexterity saving throw or take 21 (3d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Lair Actions

On initiative count 20 (losing initiative ties), the dragon takes a lair action to cause one of the following effects; the dragon can’t use the same effect two rounds in a row:  

• The dragon creates stone wall as if it had cast the Wall of Stone spell. The wall lasts for a minute or until the dragon uses this action again.
• A tremor shakes the lair in a 60-foot radius around the dragon. Each creature other than the dragon on the ground in that area must succeed on a DC 17 Dexterity saving throw or be knocked prone.
• An immobile, faintly shimmering barrier springs into existence in a 15-foot radius around a point in the lair and remains for a minute or until the dragon uses this action again. Any spell of 6th level or lower cast from outside the barrier can’t affect creatures or objects within it, even if the spell is cast using a higher level spell slot. Such a spell can target creatures and objects within the barrier, but the spell has no effect on them. Similarly, the area within the barrier is excluded from the areas affected by such spells.

Adamantine Dragons make their lairs in places with an abundance of exposed natural stone, weather by burrowing underground, into a mountains or by finding natural caverns. These lairs often include forges and enchanting stations, as the dragons feel a connection to their metals use in these fields.

Regional Effects

The region containing a legendary adamantine dragon’s lair is warped by the dragon’s magic, which creates one or more of the following effects.  

• Natural stone within 6 miles of the lair grows plentiful veins of adamantine ore, particularly underground.
• Within 6 miles of the lair, mending is cast on random objects at dawn, each creature has it cast one one object it is wearing or carrying. 1d20 objects that aren't being worn or carried have it cast on them.
• Metal is unnaturally easy to forge, work and enchant within the lair.
• Within 1 mile of the lair, whenever a creature finishes a short rest it gains temporary hit points equal to the dragons constitution modifier.

Suggested Environments

Adamantine Dragons do not naturally exist and can only occur as a product of injecting molten adamantine into a true dragon egg. They seek out isolated, rocky environments to settle.