You are a hunter that has learned the secrets of the sea and you are able to use it to help combat enemies

Critical Flow and Sea Snares

Starting at 3rd level whenever you move at least 15ft during your turn your next attack will also crit if you get a 19.
Starting at 3rd level you gain the ability Sea Snares were you confine your enemy within a tight pressurized water donut. You can use your action to try to restrain an enemy with a sea snare until the end of your next turn. The creature will have to pass a Strength saving throw of 18. On a fail they are restrained until the end of your next turn, but if they pass they aren't restrained and take 1d6 of force damage. You may only use this a number of times = to your proficiency modifier per short rest.

Merulina

Starting at 7th level you can summon your aquatic companion to help you fight. You can summon her once per long rest. Her hp is = to double your maximum hp and she shares the same AC as you, she has a movement speed of 75ft. While riding her you take a quarter of the damage you would of taken if you were on the ground,

Aquablades

Starting at 11th level you can summon sawblades made of pressurized water to help protect you. You can summon them as a bonus action and they circle around you and last until the end of your next turn. You can summon aquablades a number of times = to your wisdom modifier per long rest. They deal 2d6 magical slashing damage to anyone within 10 ft of you and they impose disadvantage on ranged attacks made against you. A melee attacker may try to push through them to attack you, to do so they must make a strength saving throw of 18 or be launched back 15 feet and proned as well as taking the 2d6 of magical slashing.

RipTide

Starting at 15th level you gain you culmination of you studies and experiences in the form of a devastating attack. Twice per long rest you can call upon the RipTide, it is an attack that you can choose a point with 60ft of you that has an area of effect of 20ft. Those who caught in the blast take 3d10 force damage however for each person caught in the blast you can add an additional d10 of force damage. Those who are hit with the attack are sent flying in a random direction for 40ft and are proned.