Ancient River Dragon

Amphibious. The dragon can breathe air and water.

Flowing Grace. The dragon doesnt provoke opportunity attacks when it flies or swims out of an enemys reach.

Legendary Resistance (3/Day). When the dragon fails a saving throw, it can choose to succeed instead. When it does, it loses coordination as white-crested waves run up and down its body. It loses its Flowing Grace and Shimmering Scales traits until the beginning of its next turn.

Shimmering Scales. While in water, the dragon gains three-quarters cover from attacks made by creatures more than 30 feet away.

Essence Link. The essence dragon is spiritually linked to a specific area or landmark. The dragon gains no benefit from a long rest when more than 1 mile away from its linked area. If the dragon dies, the area it is linked to loses its vital essence until it forms a new essence dragon, which can take centuries. When a creature first enters an area that has lost its vital essence in this way, they gain a level of fatigue and a level of strife. This fatigue and strife can be removed only by completing a long rest outside the area.

Innate Spellcasting. The dragons spellcasting ability is Charisma (save DC 20). It can innately cast the following spells, requiring no material components. 3/day each:create or destroy water, fog cloud, control water, freedom of movement, 1/day each:control weather, wall of ice

Multiattack. The dragon attacks once with its bite and twice with its claws.

Bite. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 29 (4d10 + 7) piercing damage.

Claws. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 20 (3d8 + 7) slashing damage.

Torrential Breath (Recharge 5-6). The dragon exhales water in a 90-foot-long 10-foot-wide line. Each creature in the area makes a DC 20 Dexterity saving throw taking 66 (19d6) bludgeoning damage on a failed save or half damage on a success. A creature that fails the save is also knocked prone and is pushed up to 60 feet away. A creature that impacts a solid object takes an extra 21 (6d6) bludgeoning damage.

Whirlpool. A cylindrical, 15-foot-tall, 10-foot-radius whirlpool or waterspout magically appears in the water or air, centered on a point within 60 feet. Creatures in the area make a DC 20 Strength saving throw. On a failure, a creature takes 35 (10d6) bludgeoning damage and is knocked prone and pushed up to 15 feet. On a failure, a creature takes half damage.

Snap Back (While Bloodied). When a creature the dragon can see hits it with a melee weapon attack, the dragon makes a bite attack against the attacker.

The dragon can take 3 legendary actions. Only one legendary action can be used at a time and only at the end of another creatures turn. It regains spent legendary actions at the start of its turn.

Dart Away. The dragon swims up to half its speed.

Lurk. The dragon takes the Hide action.

River Surge (Costs 2 Actions). The dragon generates a 20-foot-tall, 100-foot-wide wave on the surface of water within 120 feet. The wave travels up to 60 feet in any direction the dragon chooses and crashes down, carrying Huge or smaller creatures and vehicles with it. Vehicles moved in this way have a 25 percent chance of capsizing. Creatures that impact a solid object take 35 (10d6) bludgeoning damage.

Sudden Maelstrom (While Bloodied. The dragon magically surrounds itself with a 60-foot-radius maelstrom of surging wind and rain for 1 minute. A creature other than the dragon that starts its turn in the maelstrom or enters it for the first time on a turn makes a DC 20 Strength saving throw. On a failed save, the creature takes 28 (8d6) bludgeoning damage and is knocked prone and pushed 15 feet away from the dragon.