Deep Waters Domain

Some deities dwell not in the heavens, but in the deep,
dark recesses of the world, where life is absent but for
a few resilient, incomprehensible beings. Some clerics
draw their power from such deities, pledging their
lives to the unfathomable powers of the ocean, vowing
to become one with the eternal ebb and flow of the
tides, protecting the deep seas and the many secrets
contained therein.

Bonus Proficiency

When you choose this domain at 1st level, you gain proficiency with heavy armor.

Barnacle Barrier

You call upon the deep to manifest a shield of barnacles over your skin, which grants you Temporary Hit Points equal to twice your Cleric level.

Channel Divinity: Grip of the Fathomless

You present your holy symbol, and a crushing aura falls on a point you can see within 60 ft. The aura has a 20 ft. radius and it lasts for 1 Minute or until you are Incapacitated or die. Creatures of your choice within the aura are under extreme pressure and can only move at half Speed. If the creature is underwater, they take 1d4 Force Damage if they start their turn inside the aura.
On each of your turns after you use this feature, you can use an Action to move the aura 30 ft. in any direction.

When a creature enters the aura for the first time on a turn or starts their turn there, they must make a Constitution Saving Throw (Cleric Spellcasting DC).
On Failure: The target may only take an Action or a
Bonus Action during their turn.

Thalassic Soul

Your connection with the seas grants you special abilities. You gain Resistance to Cold Damage. You gain a Swim Speed equal to your Walk Speed, you can breathe underwater, and being underwater imposes no penalties on your Attack Rolls.

Divine Strike

At 8th level, you gain the ability to infuse your weapon strikes with divine energy. Once on each of your turns when you hit a creature with a weapon attack, you can cause the attack to deal an extra 1d8 radiant damage to the target. When you reach 14th level, the extra damage increases to 2d8.

Harbinger of Drowning

You choose a creature within 60 ft. of you that you can see and cause them to make a Constitution Saving Throw (Cleric Spellcasting DC).
On Failure: The target takes 4d8 Force Damage and is considered Grappled for 1 Minute. While Grappled in this way, the target is also considered Restrained, Blinded, and unable to breathe as they become engulfed in a torrent of water. The target can repeat the Saving Throw at the end of each of their turns, ending the effect on themselves on a success.
On Success: The target takes half as much damage and suffers no further effect.