Uro, Titan of Nature's Wrath

Nature's Wrath (Mythic Trait; Recharges after a Short or Long rest).  If Uro, Titan of Nature's Wrath is reduced to 0 Hit Points, he does not die or fall unconscious. Instead, he regains 630 Hit Points and the storm surrounding him begins to rage even harder, allowing him to now make his Lightning Strike Legendary Action in addition to his three Tempest Slam attacks each turn. Using Lightning Strike this way does not consume any Legendary Actions for the turn. 

Air Form. Uro, Titan of Nature's Wrath can enter a hostile creature's space and stop there. It can move through a space as narrow as 1 inch wide without squeezing.

Legendary Resistance (3 per day).  If Uro, Titan of Nature's Wrath fails a Saving Throw, it can choose to succeed instead.

Living Storm. Uro, Titan of Nature's Wrath is always at the center of a storm 1d6 + 4 miles in diameter. Heavy precipitation in the form of rain falls there, causing the area to be lightly obscured. The rain also extinguishes any open flames and imposes disadvantage on Wisdom (Perception) checks that rely on hearing. In addition, strong winds swirl in the area covered by the storm. The winds impose disadvantage on all ranged attack rolls and disperses fog.

Magic Resistance. Uro, Titan of Nature's Wrath has advantage on Saving Throws against spells and other magical effects.

Master of Nature. Uro, Titan of Nature's Wrath's Lightning damage ignores Resistance and Immunity.

Siege Monster. Uro, Titan of Natures Wrath deals double damage to objects and structures. 

Titan's Soul. Due to Uro, Titan of Nature's Wrath's divine nature, he cannot be killed permanently by normal means. Uro regains 40 Hit Points at the beginning of each of his turns. When reduced to 0 Hit Points while using his Mythic Trait he does not regain Hit Points. Instead, Uro falls over into an unconscious state, and will rise from his resting place with full Hit Points 10 days later. This effect cannot be stopped by any means, except by reducing Uro's Hit Points to 0 Hit Points with the Godsend Artifact; or by using a wish spell to remove this ability. 

Multiattack. Uro, Titan of Natures Wrath makes three Tempest Slam attacks.

Tempest Slam. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 24 (4d8 + 10) bludgeoning damage and 24 (4d8 +10) lightning damage. The target must make a DC 23 Strength Saving Throw or be pushed 20 feet away from Uro, Titan of Nature's Wrath in any direction.

Whirlwind (Recharge 3–6). Each creature in Uro's space must make a DC 23 Strength saving throw. On a failure, a target takes 55 (10d8 + 10) bludgeoning damage and is flung up 60 feet away from Uro in a random direction and knocked prone. If a thrown target strikes an object, such as a wall or floor, the target takes 3 (1d6) bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a DC 23 Dexterity saving throw or take the same damage and be knocked prone.

If the saving throw is successful, the target takes half the bludgeoning damage and isn't flung away or knocked prone.

Lightning Storm (Recharge 6). All other creatures and structures within Uro's Living Storm radius must make a DC 23 Dexterity Saving Throw, taking 82 (16d8 + 10) Lightning damage on a failed save, or half as much damage on a successful one (Structures automatically fail the Saving Throw). If a target creature fails the Saving Throw by 5 or more, the creature is also stunned until the end of its next turn. 

Uro, Titan of Nature's Wrath 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 creatures turn. Uro, Titan of Nature's Wrath regains any spent Legendary Actions at the start of its turn.

Move. Uro, Titan of Nature's Wrath moves up to its speed.

Tempest Slam. Uro, Titan of Nature's Wrath makes one Tempest Slam attack.

Lightning Strike (Costs 2 Actions). Uro, Titan of Nature's Wrath can cause a bolt of Lightning to strike a point on the ground anywhere under its Living Storm. Each creature within 5 feet of that point must make a DC 23 Dexterity Saving Throw, taking 26 (3d10 + 10) Lightning damage on a failed save, or half as much on a successful one. 

If Uro, Titan of Nature's Wrath's Mythic Trait is active, he can use the options below as Legendary Actions for 1 hour after using Nature's Wrath.

Maelstrom Surge (Costs 2 Actions). Uro, Titan of Nature's Wrath can cause an enormous surge of water to pool towards him, all other creatures and structures within 120ft of Uro make a DC 23 Strength Saving Throw or take (4d6 + 10) Bludgeoning damage and being pulled 60 feet towards Uro and knocked prone. On a success, the target takes half as much damage and is only pulled 30ft. Structures fail this save automatically. After this ability is used, the water level in the area of Uro's Living Storm rises by 20-feet, but does not rise higher on subsequent uses.

Screaming Gale (Costs 3 Actions). Uro, Titan of Nature's Wrath releases a blast of Thunder, Wind, and Rain in a line that is 1 mile long and 20ft Wide. Creatures in that area must succeed on a DC 23 Dexterity Saving Throw or take 36 (4d12 +10) Thunder Damage and be flung up to 60 feet in the direction of the line. If a thrown target collides with an immovable object, such as a wall or floor, the target takes 3 (1d6) bludgeoning damage for every 10 feet it was thrown before impact. If the target would collide with another creature instead, that other creature must succeed on a DC 20 Dexterity Saving Throw or take the same damage and be knocked prone. Objects and Structures in the area of effect automatically fail the Saving Throw.