Amphibious. The dragon can breathe air and water.

Spellcasting. The emerald dragon is an innate spellcaster. Each spell can be cast once per day, requiring no material components. Its spellcasting ability is Charisma (spell save DC 16, +8 to hit with spell attacks). The emerald dragon has the following spells prepared:

3rd level: dispel magic

4th level: fire shield

5th level: dominate person

Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

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: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 7 (2d6) poison damage.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) 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 16 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.

Breath Weapons (Recharge 5-6). The dragon uses one of the following breath weapons.

Poison Breath. The dragon exhales poisonous gas in a 60-foot cone. Each creature in that area must make a DC 18 Constitution saving throw, taking 56 (16d6) poison damage on a failed save, or half as much damage on a successful one.

Sleep Breath. The dragon exhales sleep gas in a 60-foot cone. Each creature in that area must succeed on a DC 18 Constitution saving throw or fall unconscious for 10 minutes. This effect ends for a creature if the creature takes damage or someone uses an action to wake 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.

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 10 feet of the dragon must succeed on a DC 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.