Adult Purple Pearl Dragon

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

Tail. Melee Weapon Attack: +10 to hit, reach 20 ft., one target. Hit: 14 (2d8 + 5) bludgeoning damage.

Constrict. Melee Weapon Attack: +10 to hit, reach 5 ft., one creature. Hit: 21 (6d6 + 5)bludgeoning damage, and the target is grappled (escape DC 19). Until this grapple ends, the creature is restrained, and the dragon can't constrict another target.

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 19 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.

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 60-foot cone. Each creature in that area must make a DC 19 Constitution saving throw, taking 45 (13d6) 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.

Lightning Breath (Recharge 6 only). The dragon exhales lightning in a 90-­foot line that is 5 feet wide. Each creature in that line must make a DC 19 Dexterity saving throw, taking 66 (12d10) lightning damage on a failed save, or half as much damage on a successful one.

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.

Constrict. The dragon Constricts.

Consume Positive Magics; Pearl dragons have the unique ability to Consume/be empowered by different things, and convert the energy from that into pearls for their horde. Purple Pearls are able to use their reaction to Absorb spells that have positive effects on their enemies during combat, Such as Healing Spells, and Spells of protection etc. They can even Undue the effects of Beneficial magic items, and are happy to eat such things.