Uro

Nature's Wrath (Mythic Trait; Recharges after a Short or Long Rest). When Uro is reduced to 0 hit points, he doesn’t die or fall unconscious. Instead, he regains 676 hit points and casts the tsunami spell. The spell save DC for the spell is 20.

Legendary Resistance (3/Day). If Uro fails a saving throw, he can choose to succeed instead.

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

Siege Monster. Uro deals double damage to objects and structures.

Multiattack. Uro can use his Frightful Presence. He then makes five attacks with his fist.

Fist. Melee Weapon Attack: +19 to hit, reach 15ft., one target. Hit: 28 (4d8 + 10) bludgeoning damage.

Frightful Presence. Each creature of Uro choice within 120 feet of him and aware of him must succeed on a DC 17 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if Uro is within line of sight, 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 Uro's Frightful Presence for the next 24 hours.

Flood. Uro casts the tsunami spell. The spell save DC for the spell is 20.

Uro 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. Uro regains spent legendary actions at the start of his turn. 

Attack. Uro makes one fist attack.

Detect. Uro makes a Wisdom (Perception) check.

Move. Uro moves up to half his speed.

If Uro mythic trait is active, it can use the options below as legendary actions for 1 hour after using Nature's Wrath.

Flood. Uro casts the wall of water spell. 

Benthic Movement (Costs 2 Actions). Uro makes a fist attack, casts the wall of water, and moves up to half of his speed.