Ancient Pearl Dragon

Amphibious. The dragon can breathe air and water.

Aura of Tranquility. Friendly creatures of the dragon’s choice within 60 feet gain advantage on all saving throws and resistance to psychic damage. Enemies of the dragon’s choice in the aura have disadvantage on saving throws against being frightened.

Luminous Dominion. The dragon sheds bright light in a 60-foot radius and dim light for an additional 60 feet. Enemies that start their turn in the bright light must succeed on a DC 20 Wisdom saving throw or have disadvantage on attack rolls until the start of their next turn.

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

Magic Resistance. The dragon has advantage on saving throws against spells and other magical effects.

Mythic Trait: Avatar of the Pearl Tide (Optional)
When the dragon is reduced to 0 hit points, it does not die. Instead, it shatters into radiant water and reforms, regaining 150 hit points. All conditions affecting it end.
When this trait activates:

• Pearl Breath recharges immediately
• The dragon emits a Healing Surge, restoring 30 hit points to all allies within 60 feet
• The battlefield becomes lightly obscured by shimmering mist for enemies (no effect on allies)

Multiattack. The dragon makes three attacks: one with its bite and two with its claws. It can replace one claw attack with a tail attack.

Bite. Melee Weapon Attack: +15 to hit, reach 15 ft., one target.
Hit: 25 (2d12 + 8) piercing damage plus 16 (3d10) radiant damage.

Claw. Melee Weapon Attack: +15 to hit, reach 10 ft., one target.
Hit: 17 (2d8 + 8) slashing damage.

Tail. Melee Weapon Attack: +15 to hit, reach 20 ft., one target.
Hit: 19 (2d10 + 8) bludgeoning damage.

Pearl Breath (Recharge 5–6). The dragon exhales radiant tidal force in a 90-foot cone.

• Enemies must make a DC 22 Dexterity saving throw, taking 81 (18d8) radiant damage on a failed save, or half as much on a success.
• Allies in the cone instead regain 45 (10d8) hit points and can end one condition affecting them (charmed, frightened, or poisoned).

Tidal Cataclysm (Recharge 5–6). The dragon calls forth a devastating wave in a 60-foot radius centered on a point it can see within 120 feet.

• Enemies must make a DC 22 Strength saving throw or take 45 (10d8) bludgeoning damage, be knocked prone, and pushed up to 30 feet. On a success, they take half damage and aren’t moved.
• Allies instead can reposition up to 30 feet and gain 20 temporary hit points.

Tide Step. While in water, the dragon moves up to 60 feet without provoking opportunity attacks.

Perfect Serenity. The dragon targets up to three creatures it can see within 60 feet. Each target gains 15 temporary hit points and can immediately reroll a failed saving throw.

Protective Pulse. When a creature the dragon can see within 60 feet takes damage, the dragon reduces that damage by 4d8 + 7.

Radiant Rebuke. When the dragon is hit by an attack, the attacker takes 14 (4d6) radiant damage.

Legendary Actions

The dragon can take 3 legendary actions, choosing from the options below. It can take only one legendary action at a time and only at the end of another creature’s turn. The dragon regains all spent legendary actions at the start of its turn.

• Detect. The dragon makes a Wisdom (Perception) check, adding its Perception bonus to the roll to spot hidden creatures, notice subtle details, or otherwise observe its surroundings.
• Tail Attack. Melee Weapon Attack: +15 to hit, reach 20 ft., one target.
  Hit: 19 (2d10 + 8) bludgeoning damage.
• Shimmering Shift (Costs 2 Actions). The dragon moves up to half its speed without provoking opportunity attacks.
• Calm Pulse (Costs 2 Actions). Creatures of the dragon’s choice within 60 feet regain 18 (4d8) hit points.
• Radiant Wave (Costs 3 Actions). Creatures of the dragon’s choice within 30 feet must make a DC 20 Constitution saving throw, taking 18 (4d8) radiant damage and becoming blinded until the end of their next turn on a failed save, or taking half as much damage and not being blinded on a successful one.

While Avatar of the Pearl Tide is Active
The dragon gains access to the following legendary action option:

Mythic Tide (Costs 3 Actions). The dragon unleashes a wave of radiant force. Enemies of its choice within 60 feet must make a DC 22 Dexterity saving throw, taking 27 (6d8) radiant damage and being knocked prone on a failure, or half as much on a success. Allies instead regain 18 (4d8) hit points.