Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.
Psionics. The dragon has aura sight, psychometry, precognition, clairsentience, ESP, and life detection.
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: +10 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage.
Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.
Tail. Melee Weapon Attack: +10 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.
Fog Cloud. The dragon creates a 30-foot-radius sphere of fog centered on a point within range. The sphere spreads around corners, and its area is heavily obscured. It lasts for 5 (2d4) turns or until a wind of moderate or greater speed (at least 10 miles per hour) disperses it.
Sonic Breath (Recharge 5–6). The dragon exhales sonic in a 120-foot cone. Each creature in that area must make a DC 18 Constitution saving throw, taking 36 (12d4+6) thunder damage on a failed save, or half as much damage on a successful one. They must also make a second save or be stunned. Each creature can repeat the save at the end of its turn with advantage to end the stun.
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.
Description
Emerald dragons are curious and inquisitive creatures, with many being wiser and more intelligent than many sages. They are also known for being very paranoid. They have shimmering green scales that cause the dragon to appear as if it is in constant motion. They will eat almost anything, and are hostile towards nearby fire giants, which they often come into contact with.
Lair and Lair Actions
Emerald dragons live in tropical or subtropical climates. They either live near civilization, though not too close, or in extinct volcanoes, and keep their presence relatively unknown. They occasionally live near sapphire dragons
Emerald dragons are very paranoid and distrustful, so their lairs have many traps spread throughout. The dm may choose the nature of these traps while keeping in mind that they were put in place by a dragon. The activation of these traps depends on their nature and requires no action by the dragon.
Main source of information: http://www.mojobob.com/roleplay/monstrousmanual/d/drageeme.html. (This info is for the 2e emerald dragon. Look elsewhere for the 3e version.)