Chiang Lung (River Dragon)

Innate Spellcasting. The dragon’s spellcasting ability is Charisma (spell save DC 16, +8 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

• At will: augury, bless, bane, control water, control winds, dispel evil and good, detect thoughts,divination, invisibility, plane shift (Any Spirit Realm/Ningen-Do only)
• divination, master of the rolling river (as wall of water), remove curse
• 3/day each: polymorph (self only, humanoid form only)
• 1/day each: creation 

Fly. Though wingless, chiang lungs can fly magically due to a magic blue pearl embedded in their brains. If removed from the dragon, this pearl loses its magic but is still worth 1,000 gp. The dragon can cease or resume flight as a free action.

Keen Senses. The dragon has advantage on Wisdom (Perception) checks.

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

Sea King’s Blessing. The dragon can breathe air and water. Any creature in physical contact with a chiang lung can also breathe and move underwater as if affected by the spells water breathing and freedom of movement.

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 4 (1d8) water (bludgeoning) 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.

Cause Rain (Recharge 5–6). A chiang lung can breathe storm clouds, causing rain whenever and wherever it chooses. The rain lasts for 2d4 hours and extends in a two-mile radius centred on the dragon. Alternatively it can concentrate this breath weapon. The dragon can use this ability offensively by concentrating the storms which acts as a storm sphere (6th level spell).

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 Slap. The dragon makes a tail attack.
• Crush (Costs 2 Actions). The dragon uses its girth to crush a creature by dropping from the sky. Each creature within a 15-foot sphere centred on 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.

Both the adult and the ancient Chiang Lung have access to the same lair actions and regional effects

(NB. These are placeholders only!, still need to work on these).

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:

• Pools of water that the dragon can see within 120 feet of it surge outward in a grasping tide. Any creature on the ground within 20 feet of such a pool must succeed on a DC 15 Strength saving throw or be pulled up to 20 feet into the water and knocked prone.
• A cloud of swarming insects fills a 20-foot-radius sphere centered on a point the dragon chooses within 120 feet of it. The cloud spreads around corners and remains until the dragon dismisses it as an action, uses this lair action again, or dies. The cloud is lightly obscured. Any creature in the cloud when it appears must make on a DC 15 Constitution saving throw, taking 10 (3d6) piercing damage on a failed save, or half as much damage on a successful one. A creature that ends its turn in the cloud takes 10 (3d6) piercing damage.
• Magical darkness spreads from a point the dragon chooses within 60 feet of it, filling a 15-foot-radius sphere until the dragon dismisses it as an action, uses this lair action again, or dies. The darkness spreads around corners. A creature with darkvision can’t see through this darkness, and nonmagical light can’t illuminate it. If any of the effect’s area overlaps with an area of light created by a spell of 2nd level or lower, the spell that created the light is dispelled.

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:

• The land within 6 miles of the lair takes twice as long as normal to traverse, since the plants grow thick and twisted, and the swamps are thick with reeking mud.
• Water sources within 1 mile of the lair are supernaturally fouled. Enemies of the dragon that drink such water regurgitate it within minutes.
• Fog lightly obscures the land within 6 miles of the lair.

If the dragon dies, vegetation remains as it has grown, but other effects fade over 1d10 days.