5th Edition Aquatic Builds (Cleric)

The only domain available to clerics that most closely duplicates worship of sea gods is the Tempest domain. Gods of storms and seas are common across pantheons, though the Tempest domain leans far more toward gods like Thor than they do Poseidon.

Below you will find a variant of the Tempest domain that grants the cleric power over marine creatures as well as the ocean and weather.

Oceanic Domain

Oceanic Domain Spells

1st: fog cloud, speak with animals

3rd: alter self, gust of wind
5th: call lightning, water breathing
7th: control water, dominate beast
9th: conjure elemental, destructive wave

Bonus proficiencies

Athletics, Nature, tridents, nets

Wrath of the Storm

At 1st level, you can thunderously rebuke attackers. When a creature within 5 feet of you that you can see hits you with an attack, you can use your reaction to cause the creature to make a Dexterity saving throw. The creature takes 2d8 lightning or thunder damage (your choice) on a failed saving throw, and half as much damage on a successful one.

You can use this feature a number of times equal to your Wisdom modifier (minimum once). You regain all expended uses when you finish a long rest.

Channel Divinity: Lord of the Sea

At 2nd level you may use your Channel Divinity to charm any and all marine creatures within 30 feet of you.

As an action, you present your holy symbol and invoke the name of your deity. Each creature must make a Charisma saving throw. Any creatures that fail the save are charmed by you for 1 hour or until they take damage. This applies to all fresh and salt water creatures as well as to marine birds and marine mammals (including transitional mammals such as polar bears and otters). Plant creatures composed of seaweed or swamp foliage and intelligent creatures, such as merfolk, may also be targeted by this power, though they have advantage on the saving throw and may repeat the save every 10 minutes until the power expires. Unlike other charm powers, this ability affects swarms composed of these creatures, such as a swarm of quippers. While the creatures are charmed, they are friendly to you and other creatures you designate.

Channel Divinity: Sea Blessing

At 6th level, you may use your Channel Divinity to grant yourself and all allies within 30 feet the sea's blessing. Any creature may expend their blessing to gain Advantage on one of the following checks: saves against cold, saves against lightning, saves against thunder, Dexterity (Acrobatics), or Strength (Athletics). Sea's blessing lasts one hour or until expended. Those targeted may choose which roll to use the Advantage on and they need not remain within 30 feet of you to retain this bonus. A character may only have one sea blessing at a time. If the cleric uses this ability again, any blessings still active are dismissed at the end of the following round.

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 damage to target. This damage may be cold, lightning or thunder damage (your choice). When you reach 14th level, the extra damage does not increase. Instead, all targets that are hostile to you and are within 10 feet of the target must make a Constitution save or take the same amount and type of damage as the target. If used underwater, the targets of the area damage have disadvantage on the saving throw.

Sea Lord:

At 17th level, when using the Sea's Blessing Channel Divinity power, targets may gain Advantage on three checks or saves before it is expended and the blessing lasts 12 hours instead of 1. In addition, plants and intelligent marine creatures, such as merfolk, no longer have Advantage on saves against the Lord of the Sea Channel Divinity power.