"The Dragon of the Year Edition has more dragon than ever before" - IGN
"Adult Green-Emerald Dragon is a triumph" - metacritic
"Legendary even without the legendary actions" - gamesradar

An anomaly infused with unnatural magic ability. Green-emerald dragons are a combination of cunning, manipulation, and always curiousity. Green-emerald dragons use illusory magics and natural concealment abilities to make their presence (and existence) almost impossible to discern. A green-emerald dragon is marked by deep green scales gilded with the shimmering emerald for which half of its ancestry is owed. They are somewhat less physically strong than either of their progenitors, however their magical aptitude, intelligence, and mental fortitude are undeniably (and dangerously) superior.

Green-emerald dragons prize knowledge, particularly local histories and Intel that can be gleamed from it. They usually know of places of power near their lairs and keep detailed records of how phenomena connected to those sites react to outside influences. They also avidly collect magic items and spells that create illusions, allowing them to better conceal their treasures from prying eyes and divinations. Their parentage bestows proficiency in burrowing and swimming proficiently, though to a more moderate ability. In the air are physically slower than other dragons however make up for this with spells that supplement their level of agility when needed. They are found to be sensitive high levels of noise which  lends itself to their tendency to be isolated from others. It is theorized that this may also be due to their heightened  sensitivities. The fierce loyalty to their kin that comes from their green dragon ancestry takes the form of wanting to safeguard their lives, to ensure the stories of their kin continue.

It is said that the green-emerald dragon will choose the most remote forests, adjacent to perilous mountains in regions with moderate volcanic activity beneath the earth's surface. Hot springs within the forest or along the mountain walls are often found near an green-emerald dragon's lair. Unlike green dragons, a forest controlled by a green-emerald dragon is not quite as easy to spot. If left unattended to by the dragon the same perpetual fog will hang in the air within and even beyond the forest. The green-emerald dragon maintains the ability to mask these symptoms of its presence utterly, if it should choose. The moss-covered trees grow close together except where winding pathways trace their way like a maze into the heart of the forest. The light that reaches the forest floor carries an emerald green cast, and every sound seems muffled. 

At the edge of the forest but base of the mountain the dragon chooses a cave in a sheer cliff or hillside for its lair, preferring an entrance hidden from prying eyes. Some seek out cave mouths concealed behind waterfalls, or partly submerged caverns that can be accessed through lakes or streams. The caves then become an additional labyrinth of tunnels. The dragon often seeks cave networks with proximity to hot spring sources in mind. Thus some tunnels of the network may have tubes of unrelenting hot air or gas passing through them, creating natural obstacles to the inner lair. Deep in the inner lair, lava pools may be just beyond the cave walls, producing an ominous red glow in the rocky tunnels. The dragon designs the lair in this way intentionally because despite its ability to handle the extreme heat, it prefers not to have direct exposure to the pools of lava and instead uses them as sources to keep their homes comfortable and  warm (often too warm for other creatures).

Lair Actions

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:

• Grasping roots and vines erupt in a 20-foot radius centered on a point on the ground that the dragon can see within 120 feet of it. That area becomes difficult terrain, and each creature there must succeed on a DC 15 Strength saving throw or be restrained by the roots and vines. A creature can be freed if it or another creature takes an action to make a DC 15 Strength check and succeeds. The roots and vines wilt away when the dragon uses this lair action again or when the dragon dies.
• Distort Perceptions. The dragon attempts to alter the perceptions of one creature it can see within its lair. That creature must succeed on a DC 15 Intelligence saving throw or take 22 (4d10) psychic damage and have disadvantage on saving throws until the start of its next turn.
• Vanish. The dragon becomes invisible until initiative count 20 on the next round
• Magical fog billows around one creature the dragon can see within 120 feet of it. The creature must succeed on a DC 15 Wisdom saving throw or be charmed by the dragon until initiative count 20 on the next round.

Regional Effects

The region containing a legendary  dragon’s lair is warped by the dragon’s magic, which creates one or more of the following effects:

• Thickets and large rocks form labyrinthine passages within 1 mile of the dragon’s lair. The thickets act as 10-foot-high, 10-foot-thick walls that block line of sight. Creatures can move through the thickets, with every 1 foot a creature moves costing it 4 feet of movement. A creature in the thickets must make a DC 15 Dexterity saving throw once each round it’s in contact with the thickets or take 3 (1d6) piercing damage from thorns.
  Each 10-foot-cube of thickets has AC 5, 30 hit points, resistance to bludgeoning and piercing damage, vulnerability to fire damage, and immunity to psychic and thunder damage.
• Within 2 miles of its lair, the dragon leaves no physical evidence of its passage unless it wishes to. Tracking it there is impossible except by magical means. In addition, it ignores movement impediments and damage from plants and rocks in this area that are neither magical nor creatures, including the thickets described above. The plants remove themselves from the dragon’s path.
• Crystal Profusion. Natural stone within 4 miles of the lair grows plentiful crystal formations and veins of emerald gemstones.
• Mystic Sight. Fire and pools of water within 6 miles of the lair become conduits for the dragon’s psionic presence. As an action, the dragon can cast the clairvoyance spell, requiring no spell components and targeting any area of fire or lava in that region.
• Rodents, lizards and birds within 1 mile of the dragon’s lair serve as the dragon’s eyes and ears. Deer and other large game are strangely absent, or appear to act unusually, as if in a trance.

If the dragon dies, the rodents and birds lose their supernatural link to it. The thickets remain, but within 1d10 days, they become mundane plants and normal difficult terrain, losing their thorns. Rocks immediately stop moving of their own accord. The existing abundance of crystals and emeralds remains, but new ones form at a normal rate

The region surrounding a legendary  dragon’s lair is altered by the dragon’s magic, creating one or more of the following effects.

Subtle Obstructions. Rocks and brambles within 6 miles of the dragon’s lair sometimes move of their own accord, usually when no one is watching. Often the rocks and vines, branches or bushes obstruct the approach to the emerald dragon’s lair, with boulders moving to block narrow defiles, way-markers tumbling off the path, or smaller stones shifting beneath travelers’ feet to send them tumbling down slopes or into rivers.

Cognitive Fog: Travellers without coniction approaching the dragon's lair begin to forget their purposes in the area. They do not lose their memories but become more forgetful of actions they had meant to take and words meant to be spoken. 

Should the dragon expire, rocks and brambles immediately stop moving of their own accord. The existing abundance of plant life, crystals and emeralds remains, but new ones form at a normal rate.