Multiattack. The dragon makes three attacks: one with its bite and two with its claws. Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 3 (1d6) fire damage. Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage. Fire Breath (Recharge 5-6). The dragon exhales fire in a 30-foot cone. Each creature in that area must make a DC 17 Dexterity saving throw, taking 56 (16d6) fire damage on a failed save, or half as much damage on a successful one.
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 strikes 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.
Red dragons lair in high mountains or hills, dwelling in caverns under snow-capped peaks, or within the deep halls of abandoned mines and dwarven strongholds. Caves with volcanic or geothermal activity are the most highly prized red dragon lairs, creating hazards that hinder intruders and letting searing heat and volcanic gases wash over a dragon as it sleeps. With its hoard well-protected deep within the lair, a red dragon spends as much time outside the mountain as in it. For a red dragon, the great heights of the world are the throne from which it can look out to survey all it controls - and the wider world it seeks to control. Throughout the lair complex, servants erect monuments to the dragon's power, telling the grim story of its life, the enemies it has slain, and the nations it has conquered.
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.
Even as long-lived as they are, all dragons must eventually die. This thought doesn't sit well with many dragons, some of which allow themselves to be transformed my necromantic energy and ancient rituals into powerful undead dracoliches. Only the most narcissistic dragons choose this path, knowing that by doing so, they sever all ties to their dragon kin and the dragon gods. A dracolich retains its shape and size upon transforming, its skin and scales drawing tight to its bones or sloughing away to leave a skeletal form behind. its eyes appear as glowing points of light floating in shadowy sockets, hinting at the malevolence of its undead mind. Though many dragons pursue vain goals of destruction and dominance, dracoliches are more nefarious than the most evil dragons, driven to rule over all. A dracolich is a fiendishly intelligent tyrant that crafts complex webs of foul schemes, attracting servants motivated by greed and a lust for power. Acting from the shadows and actively plotting to keep its existence a secret, a dracolich is a cunning and challenging foe. Creating a dracolich requires the cooperation of the dragon and a group of mages or cultists that can perform the proper ritual. During the ritual, the dragon consumes a toxic brew that slays it instantly. The attendant spellcasters then ensnare its spirit and transfer it to a special gemstone that functions like a lich's phylactery. As the dragon's flesh rots away, the spirit inside the gem returns to animate the dragon's bones. If a dracolich's physical form is ever destroyed, its spirit returns to the gem as long as the two are on the same plane. If the gem comes into contact with another dragon's corpse, the dracolich's spirit can take possession of that corpse to become a new dracolich. If the dracolich's spirit gem is taken to another plane, the dracolich's spirit has nowhere to go when its undead body is destroyed and simply passes into the afterlife.
Red dragons prefer mountainous terrain, badlands, and any other locale where they can perch high and survey their domain. Their preference for mountains brings them into conflict with the hill-dwelling copper dragons from time to time.