Amphibious. The dragon can breathe both air and water.
Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.
Multiattack. The dragon uses it Frightful Presence. It then makes one Bite attack and two Claw attacks.
Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 19 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.
Bite. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 18 (2d10+7) piercing damage.
Claw. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 14 (2d6+7) slashing damage.
Immolating Breath (Recharge 5–6). The dragon exhales an intense blast of fire in a 60-foot cone. Each creature in that area must make a DC 22 Dexterity saving throw. On a failed save, the creature takes 55 (10d10) fire damage, or half as much damage on a success. A creature that fails the saving throw also begins to burn from the inside out, taking 5 (1d10) fire damage at the beginning of each of its turns. A burning creature may attempt a DC 22 Constitution saving throw at the end of each of its turns, ending the burning effect on a success.
Spellcasting (Psionics). The dragon casts one of the following spells, requiring no spell components and using Intelligence as the spellcasting ability (spell save DC 21, +13 to hit with spell attacks):
At Will: control flames
1/day each: earth tremor (at 2nd level), fireball, fire shield, scorching ray (at 3rd level)
Psychic Step. The dragon magically teleports to an unoccupied space it can see within 60 feet of it.
The 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 dragon regains spent legendary actions at the start of its turn.
Claw. The dragon makes one claw attack.
Psionics (Costs 2 Actions). The dragon uses Psychic Step or Spellcasting.
Planar Fires (Costs 3 Actions). The dragon invokes a storm from the plane of fire, appearing in a location it can see within 60 feet of it. The storm consists of up to three 10-foot cubes which can be arranged in any way the dragon chooses, so long as each cube has at least one 5-foot face touching another. Each creature within the area of the storm must succeed on a DC 21 Dexterity saving throw or take 14 (4d6) fire damage.
Lair and Lair Actions
An Obsidian Dragon’s Lair
Obsidian dragons prefer warm mountainous or subterranean environments, such as regions heavy with volcanic activity. They may lair in an active volcano, in a cavern overlooking a lake of magma, or even in the Elemental Plane of Fire. Over time, the presence of an obsidian dragon, and their tendency to frequent the Plane of Fire, drastically alters the landscape surrounding their lair. The borders between their native plane and the Plane of Fire may even become so thin that crossing from one to the other can be achieved by a mere misplaced step.
The challenge rating of a legendary obsidian dragon increases by 1 when it’s encountered in its lair.
Lair Actions
On initiative count 20 (losing initiative ties), the dragon can take one of the following lair actions; the dragon can’t take the same lair action two rounds in a row:
Dread Whisper. The dragon telepathically whispers to one creature within range of the dragon’s telepathy. The creature must succeed on a DC 15 Wisdom saving throw or be frightened by the dragon and its lair until initiative count 20 on the next round.
Firefall. The dragon causes a geyser of molten rock to erupt from a 5-foot square that it can see within 60 feet of it. Searing material falls in a 20-foot radius hemisphere centred on that location. Each creature within the area must makes a DC 15 Dexterity saving throw, taking 10 (3d6) fire damage on a failed save, or half as much damage on a success. The area becomes difficult terrain for 1 minute for any creature not resistant or immune to fire damage.
Plane Shift. The dragon plane shifts to a remote rocky outcrop in the plane of fire, or from the plane of fire to its lair. Any creature in physical contact with the dragon when it plane shifts is teleported along with it (up to a maximum of four other creatures).
Regional Effects
The region surrounding a legendary obsidian dragon’s lair is altered by the dragon’s presence, creating one or more of the following effects:
Searing Serpents. Salamanders from the plane of fire establish nests within 1 mile of the dragon’s lair, and begin to terraform the land to their liking.
Crystal Profusion. Outcrops of polished, sharp-edged obsidian form within 6 miles of the dragon's lair, with larger specimens, up to 5-foot tall, growing closer to the lair. These will often grow in such a way as to obstruct the approach to the dragon's lair.
Thriving Wildlife. Reptiles, including varieties of giant lizard and snakes, as well as other creatures that prefer warm environments are attracted to the area within 6 miles of the lair and settle there in large numbers. Other creatures may be forced out by increased predation or competition.
Glass Sight. Polished stone and obsidian surfaces within 6 miles of the lair act as a conduit for the dragon’s psionic presence. As an action, the dragon can cast the clairvoyance spell, requiring no spell components and targeting any such formation in that region.
If the dragon dies, all salamanders in the region immediately return to the plane of fire, and the changes they affected slowly revert to a more natural environment over 1d10 weeks. Meanwhile, the natural ecosystem within 6 miles returns over 1d10 days. The existing abundance of obsidian glass remains, but new ones form at a normal rate.
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