Amphibious. The dragon can breathe air and water.

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

Multiattack. The dragon can use its Calming Presence. It then makes three attacks: one with its bite and two with its tail. Or it can use it's Action to Constrict, or use a breathe attack. 

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 16 (2d10 + 5) piercing damage.

Tail. Melee Weapon Attack: +9 to hit, reach 15 ft., one target. Hit: 12 (2d6 + 5) bludgeoning damage.

Constrict. Melee Weapon Attack: +9 to hit, reach 5 ft., one creature. Hit: 19 (4d6 + 5)bludgeoning damage, and the target is grappled (escape DC 18). Until this grapple ends, the creature is restrained, and the dragon can't constrict another target.

Calming Presence. Each creature of the dragon's choice that is within 60 feet of the dragon and aware of it must succeed on a DC 17 Wisdom saving throw or become [Tooltip Not Found] for 1 minute, and is unable to attack the dragon or be angry or upset at it in any fashion unless the dragon does them harm. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success, or, if the dragon harms them or an ally of their's, the effect is ended instantly. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Calming Presence for the next 24 hours.

Breath Weapons (Recharge 5–6). The dragon uses one of the following breath weapons.

Moonlit Breath. The dragon releases a beam of moonlight in a 30-foot cone. Each creature in that area must make a DC 17 Constitution saving throw, taking 55 (10d10) Radiant damage on a failed save, or half as much damage on a successful one.

A shapechanger makes its saving throw with disadvantage. If it fails, it also instantly reverts to its original form and can't assume a different form until it leaves the spell's light.

Exhale Negative Forces; Once a Negative force has been Consumed, the Dragon may then use an action to release the spell as a breathe weapon back at a chosen target. A spell giving the same status effect as the one consumed is then exhaled as a gas in a 30-foot cone. Each creature in that area must succeed on a DC 17 saving throw of the same kind that the original spell required. Those who fail suffer the same status effect that the spell once had

The dragon can take 2 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.

Constrict. The dragon Constricts.

Consume Negative Forces; Pearl dragons have the unique ability to Consume different things, and convert the energy from that into pearls for their horde...however, Black Pearls alone are able to store this energy within their bodies, and use it as a weapon to defend themselves as well as convert it to pearls to keep themselves from being overwhelmed by storing too much Negative Energy.

As a Reaction, the dragon can Consume a spell targeting itself or another creature that  applies a status effect. (These dragons can also consume curses, illnesses, poisons, corruption, and insanity).