Chou Dragon

Ascendant Form. While the Dragon is Bloodied, it can use its Toughened Hide Reaction.

Legendary Resistance (2/Day,). If the dragon fails a saving throw, it can choose to succeed instead. 

Lucky Number. Whenever the dragon rolls a 2 on a d12, the undergrowth around it grows rapidly. Each creature the Dragon chooses within 30 feet of the creature must make a DC 16 Strength Saving Throw. On a failed save, the target is Restrained. The target or a creature within reach can take an action to try and free the target from the undergrowth, doing so by succeeding on a DC 16 Strength (Athletics) check.

Undaunted. The Dragon's Speed can't be reduced, and Difficult Terrain doesn't cost extra movement.

Multiattack. The dragon makes two Hoof attacks. It can replace one attack with a Horn attack.

Hoof. Melee Attack Roll: +8, reach 5 ft. Hit: 11 (2d6 + 4) Bludgeoning damage.

Horn. Melee Attack Roll: +8, reach 10 ft. Hit: 9 (1d10 + 4) Piercing damage. If the target is a Huge or smaller creature and the Dragon has moved more than 20 feet straight towards the target immediately before the hit, the target takes an extra 6 (1d12) Piercing damage, and it is Grappled (Escape DC 16) by one of two horns.

Evoke Steadiness. The Dragon magnifies the steadiness of another creature it can see within 60 feet of itself. That creature's size increases by one category. The creature also has Advantage on Strength-based D20 Tests, and can't be moved or knocked Prone against its will. These benefits last for 1 hour, until the dragon becomes Incapacitated, or until the dragon takes this bonus action again.

Toughened Hide (Ascendant Form Only). Trigger: The dragon is hit with an attack while bloodied. Response: The attack's damage is reduced by 1d12.

Legendary Action Uses: 2. Immediately after another creature's turn, the dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each of its turns.

Charge. The dragon moves up to its Speed and makes one Horn attack.

Hoist. Vines and foliage along the dragon's back extend to enwrap a nearby Large or smaller creature within 15 feet of the dragon. The target must succeed on a DC 16 Strength Saving Throw or be pulled onto the dragon's back and is Grappled (Escape DC 16). The dragon can have one creature Grappled in this way at a time.

Overgrowth. The dragon causes nearby undergrowth to surge the ground in a 30-foot radius Sphere centered on a point the dragon can see within 30 feet of it. The area is difficult terrain.