Legendary Resistance (3/Day).

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

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: 21 (2d10 + 10) piercing damage plus 14 (4d6) fire damage.

Claw.

Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 17 (2d6 + 10) slashing damage.

Tail.

Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage.

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 21 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.

Fire Breath (Recharge 5–6).

The dragon exhales fire in a 90-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 91 (26d6) fire damage on a failed save, or half as much damage on a successful one.

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.
Tail Attack. The dragon makes a tail attack.
Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 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:

Magma erupts from a point on the ground the dragon can see within 120 feet of it, creating a 20-foot-high, 5-foot-radius geyser. Each creature in the geyser's area must make a DC 15 Dexterity saving throw, taking 21 (6d6) fire damage on a failed save, or half as much damage on a successful one.
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 15 Dexterity saving throw or be knocked prone.
Volcanic gases form a cloud in a 20-foot-radius sphere centered on a point the dragon can see within 120 feet of it. The sphere spreads around corners, and its area is lightly obscured. It lasts until initiative count 20 on the next round. Each creature that starts its turn in the cloud must succeed on a DC 13 Constitution saving throw or be poisoned until the end of its turn. While poisoned in this way, a creature is incapacitated.

Additional Lair Actions[–]

At your discretion, a legendary (adult or ancient) red dragon can use one or both of the following additional lair actions while in its lair:

Noxious Smoke. A cloud of thick, dark smoke fills a 20-foot-radius sphere centered on a point the dragon can see within 120 feet of it. The sphere spreads around corners, and its area is heavily obscured. A creature other than the dragon that starts its turn in the cloud or enters it for the first time on its turn must succeed on a DC 15 Constitution saving throw or be poisoned until the end of its turn. The cloud lasts until initiative count 20 on the next round.
Searing Heat. Searing heat spreads out in a 15-foot-radius sphere centered on a point the dragon can see within 120 feet of it. Any creature that enters the affected area or starts its turn there must make a DC 15 Constitution saving throw, taking 10 (3d6) fire damage on a failed save, or half as much damage on a successful one. The heat lasts until initiative count 20 on the next round.

Regional Effects

The region containing a legendary red dragon's lair is warped by the dragon's magic, which creates one or more of the following effects:

Small earthquakes are common within 6 miles of the dragon's lair.
Water sources within 1 mile of the lair are supernaturally warm and tainted by sulfur.
Rocky fissures within 1 mile of the dragon's lair form portals to the Elemental Plane of Fire, allowing creatures of elemental fire into the world to dwell nearby.

If the dragon dies, these effects fade over the course of 1d10 days.

Additional Regional Effects[–]

Any of these effects might appear in the area around a red dragon's lair, in addition to or instead of the effects described in the Monster Manual:

Desertification. Precipitation is almost nonexistent within 6 miles of the dragon's lair, making the land parched and arid and most plant life withered and brown.
Fiery Senses. The dragon can hear up to 30 feet through any open flame within 1 mile of the dragon's lair.
Ominous Flames. Open flames within 6 miles of the dragon's lair are tinged dark red, hiss and crackle constantly, and throw off embers and showers of sparks.

Ancient Red Dragon