Ancient Green Dragon
Gargantuan Dragon, lawful evil
41,000 XP
Special Abilities
Amphibious
The dragon can breathe air and water.
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: +15 to hit, reach 15 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 10 (3d6) poison damage.
Claw
Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 22 (4d6 + 8) slashing damage.
Tail
Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) 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 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.
Poison Breath (Recharge 5-6)
The dragon exhales poisonous gas in a 90-foot cone. Each creature in that area must make a DC 22 Constitution saving throw, taking 77 (22d6) poison damage on a failed save, or half as much damage on a successful one.
Legendary Actions
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 ft. of the dragon must succeed on a DC 23 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.
Quick Reference
Running This Encounter
An Ancient Green Dragon is a deadly solo encounter that demands respect and preparation. Use legendary actions and lair actions to control pacing and prevent players from dominating action economy. The dragon should use its intelligence to manipulate the battlefield, set traps, and retreat to advantageous positions. Emphasize the dragon's arrogance and desire to toy with opponents before delivering the killing blow.
Combat Tactics
The dragon opens with breath weapon to soften the party, then uses wing attacks and tail swipes to control positioning. It leverages its legendary actions to move away from melee threats, cast spells, and make additional attacks each round. The dragon prioritizes removing spellcasters and healing support first, using its high intelligence to identify tactical threats.
Environment & Setting
An ancient green dragon thrives in dense forests, swamps, or overgrown ruins where it can use terrain for cover and ambush tactics. Underground lairs with multiple exits, perches for aerial combat, and toxic pools from the dragon's poisonous nature create ideal hunting grounds.