Vine Dragon

Plant attribute. The dragon doesn´t need to breathe, but needs to take in sunlight ,otherwise it´s health goes down by 1 for every three days without It.

Also It has different physiology than other living creatures, therefore poison, potions and other substances are only half as effective, unless they were specifically made for this creature.

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

Transform. The dragon is mostly made of plants, vines mostly, and is able to transform to some extent. It can change It´s size to Medium or Huge from It´s base Large.
This doesn´t affects any of It´s skills or attacks.

Insightful. The Dragon can tell If someone tries to deceive It. 

Example: An adventurer tells the dragon that there is an unparalleled treasure behind the mountain. Dragon thinks there is no such a thing because he/she already been there before and therefore can use this reaction to tell if the adventurere is lying.

Basically, If the dragon has an argument or a piece of information that goes against the claim, he can uncover the truth.

Magic Resistance. Has advantage on saving throws against the spells or magical effects.

Multiattack. The dragon can use its Majestic Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 20 (2d12 + 8) piercing damage.

Claw. Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 26 (4d8 + 8) slashing damage.

Tail. Melee Weapon Attack: +13 to hit, reach 25 ft., one target. Hit: 22 (2d14 + 8) bludgeoning damage.

Majestic 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 17 Charisma saving throw or become stunned 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 Majestic Presence for the next 24 hours.

Sticky Breath (Recharge 5–6). The dragon exhales sticky substence in a 70-­-foot cone. Each creature in that area must make a DC 19 Dexterity saving throw, being unable to move for the next 3 rounds on a failed save, or 1 round on a successful one.

The dragon can take 4 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.

Sweep Attack. The dragon makes a tail attack, swinging It´s tail around the area (Medium - 20ft circle, Large - 35ft circle, Huge - 50ft circle). All the creatures in the area must make a DC 19 Dexterity save, taking 18 (4d8+8) bludgeoning damage and being knocked prone on a failed save and half of that without getting knocked prone on a succesful one.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 15 feet 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.

Vine lord (Costs 2 Actions). -> This action can be used only in case there is a forest/jungle or other plant-rich biome nearby (300ft).

The dragon calls upon the plant-life in the area to build a cone around Itself, gaining full cover and next turn can choose to dig underground and move anywhere within 300ft (also gaining advantage on stealth checks). When the dragon resurfaces, all the creatures within 10 ft of It have to make a DC 17 Constitution save, being knocked prone and pushed 15 ft from the dragon on a failed save and only getting pushed on a succesful one.