You feel the most at home while you are submerged in water, Your combat prowess and ability to disappear and reappear in the blink of an eye is unparalleled while submerged. You are a master hunter of the seas and you are well known for taking on enemies far larger than yourself and living to tell the tale. 

Aquatic expertise

While underwater you gain an increase to your dexterity modifier equal to 1/3 of your rouge level rounded down. 

You also gain advantage on tracking (Nature) checks and all Charisma checks

 

Undaunted

You ignore 1 AC for every size category your target is larger than you.

Oceanic Savant

Starting at 9th level, you gain access to Abyssal dice (D6s) you gain 4 at 9th level, and you gain an extra die at 12, 15, and 18th levels. 

You can use your dice to fuel your oceanic abilities you can make 3 choices at level 9,  2 more at 15, and one last choice at 18th

Abyssal Chill

You can inflict the chill of the Deep on your foes

You halve the movement speed of any foes within your melee range

Blinding Ink

You cloak an area in squid ink for a limited time obscuring the area in darkness.

You release a cloud of squid ink that fills a 10 foot sphere with inky blackness that is treated as magical darkness, and lasts a number of rounds = to an abyssal dice roll

Crashing Waves

You bring the might of crashing waves to bear dealing bonus bludgeoning damage, and adding your abyssal dice roll to your hit:

Kraken's Grip

Your weapon causes your target to bleed as the serrated hooks on the Kraken's tentacles manifest on your weapon and shred the targets skin.

Bleed damage = 1d6+dex mod per turn

Hemorrhage: This bleed can only be stopped by active healing or first-aid given to the target by themselves or their allies.

Shadow of the Deep

You cloak yourself in the darkness of the Deep ocean. 

You affect the vision of all within sight, it is as though you are cloaked in a shadow that makes it harder to see you.

Upon activation you reduce the light level you are perceived to be in by 1 (full->dim, dim->darkness, darkness->magical darkness)

Sonar Pulse

You bring the debilitating sounds of sonar pulses to bear on your enemies. 

you loose a wave of sound in a 15 foot cone in front of you. Those in the cone must make a constitution saving throw DC(10 + proficiency bonus + abyssal dice roll)

those who fail the save are incapacitated for a number of rounds equal to your abyssal dice roll divided by 2 rounded down (1-2 = 1, 3-4 = 2, 5-6 = 3) 

Source Jump

You can move from one body of water to another within sight, soundlessly and instantaneously

you can make a stealth check during this ability and add your abyssal dice roll to the ability check

Squid Skin

You can camouflage yourself to blend in with the surrounding environment 

for 1 minute you can make a dexterity saving throw to avoid an incoming attack, DC(Hit for ranged, hit +5 for melee)

(you may use this as a bonus action OR a reaction)

Fleet Footed

Increase movement by 15 while in water and 5 while on land.

After using your action the distraction caused by whatever you did allows you to slip through your enemies without retaliation. You no longer provoke opportunity attacks until your next turn ( if you are on land this only works against a creature you have taken the attack action against. )

Improvise, Adapt, Overcome.

Starting at 17th level, you have mastered your powers and skills from the ocean and are so proficient with them you can temporarily manifest the strength you have while in the water while you are on land.

You gain all of the benefits of aquatic expertise for 6 turns.

 You also double the movement benefits of Fleet Footed ( you gain 30 feet of movement in water and 10 on land)

After 6 turns or when you choose to end it you take 1 level of exhaustion and cannot use this ability until you finish a long rest.