Actions
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.
Poison Breath (Recharge 5-6). The dragon exhales poison in a 30-foot cone. Each creature in that area must make a DC 17 Dexterity saving throw, taking 56 16d6 poison damage on a failed save, or half as much damage on a successful one.
Lair Actions
Green dragons prefer forests and caves hidden behind thickets or waterfalls on high cliffs, where they can perch high and survey their domain.
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:
Poisonous gas 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 poison 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.
Chlorine 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.
Green dragon lairs are in high cliffs, dwelling in caverns hidden by waterfalls or thickets. Caves with chlorine activity are the most highly prized green dragon lairs, creating hazards that hinder intruders and letting poisonous gases wash over a dragon as it sleeps.
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.
Regional Effects
The region containing a legendary green dragon's lair is warped by the dragon's magick, 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 poisoned.
Plants and birds develop poisonous thorns within 1 mile of the dragon's lair, allowing them to better aid the dragon.
If the dragon dies, these effects fade over the course of
1d10 days.