Adult oceanus dragon

Amphibious. The oceanus dragon can breathe air and water. 

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

Smite evil (1/day). If a creature the oceanus dragon hits with an attack is evil in alignment then the oceanus dragon can choose to deal an extra 67 (15d8) radiant damage. 

Innate Spellcasting. The adult oceanus dragon's innate spellcasting ability is Charisma (DC 16). The adult oceanus dragon can innately cast the following spells, requiring no material components:

at will: detect good and evil (evil only)

3/day each: control water, blinding smite, water breathing 

1/day each: control winds, dispel good and evil (evil only), divine word

Multi attack. The adult oceanus dragon uses its frightful presence, makes a bite attack and two claw attacks. 

Bite. Melee Weapon Attack: +13 to hit, reach 10 ft., 1 target. Hit: 18 (2d10 + 7) piercing damage.

Claw. Melee Weapon Attack: +13 to hit, reach 5 ft., 1 target. Hit: 14 (2d6 + 7) slashing damage. 

Tail. Melee Weapon Attack: +13 to hit, reach 15 ft., 1 target. Hit: 16 (2d8 + 7) bludgeoning damage. 

Frightful Presence. Each creature of the dragon’s choice that is within 120 ft. 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.

Breath Weapons (Recharges 5/6). The oceanus dragon uses one of the following breath weapons.

Lightning breath. The oceanus dragon exhales lightning in a 90ft line that is 5ft wide. Each creature win that line must make a DC 20 Dexterity saving throw or take 76 (17d8) lightning damage. On a successful saving throw a creature takes half damage. 

Tranquility gas breath. The oceanus dragon exhales a deep pink gas in a 60ft cone. Each creature within the radius must make a DC 20 Charisma saving throw or charmed by the oceanus dragon and unwilling to harm any creature. 

The adult oceanus 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 adult oceanus dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Waterborn fury (Costs 2 Actions). The oceanus dragon makes a tail attack against one creature within range that they can see and on a hit it deals an additional 13 (3d8) lightning damage and the target is grappled by the oceanus dragon.