Sea Wardens are druids who protect the waterways of their home. As the name implies, most of them operate from islands or coastal regions, but a few also have claimed large rivers or lakes as their homes. Some sea wardens embody the sea’s bounty, conducting themselves benevolently toward coastal peoples and ensuring the safety of ships coming and going. Others are bloodthirsty killers embodying the sea’s wrath who slay even subsistence fishermen who dare to sail upon their favored waterways.
At 2nd level when you select this archetype, you learn to adapt to coastal environs and are equally comfortable in the water and on land.
If you do not have a swim speed or a walking speed, you gain whichever you are missing now. If you have both, but one is slower, the slower speed increases to match the faster speed.
You can breathe air and water, and if you normally need to spend a certain amount of time in water every so often, that limitation is removed. Finally if you are roughly humanoid in shape, you can shift your form to adapt to water or land mobility. As an action, you perform a limited form of wild shape that fuses your legs into a swimming tail. If your default form has a swimming tail, you can instead split it into walking legs.
It is also impossible to disorient you in water through nonmagical means. While in the water you always know which way is north and you have an instinctive sense of how far you are from dry land in any given direction.. If you are under water, you know which way the surface is and how far you are from it
Also at 2nd level, you have trained with various weapons and skills that are especially useful in a coastal environment. You gain proficiency with nets and tridents, the Athletics skill, and the Primordial language (and its Aquan dialect). You also gain Athletics skill specialties swimming and diving. Finally, spells from the water school count as druid spells for you. You also may prepare an additional number of spells from the water school equal to your proficiency bonus.
Beginning at 6th level, you can treat water as solid ground when it suits you. You are continuously under the effects of the water walk spell, and your swim speed increases by 20 feet.
You also gain one of the following features:
Your body stores a potent electrical current. When you are hit by a melee weapon attack, you may use your reaction to deal a number of d8s of lightning damage equal to your proficiency bonus to the attacking creature.
When you use your Wild Shape to transform into a creature with both a bite attack and a swim speed, you gain an expertise die on Stealth and Athletics checks while in the water.
In addition, once per turn, you can deal extra damage when you hit a creature with a bite attack. The amount of extra damage is a number of d6s equal to half your proficiency bonus.
In order to apply this damage, you must not have disadvantage on the attack and your target must be within 5 feet of another enemy of the target who is not incapacitated. Alternatively, you can apply this damage if you have advantage on the attack.
Beginning at level 10, you gain tremendous power over nautical vessels traveling through your domain. Choose one of the following features:
All of your attacks and spells gain the Breaker weapon property against water vehicles, and you gain advantage on checks to maintain a grapple while you are in water. Also while in contact with a body of water of at least Large size, you gain temporary hit points equal to your proficiency bonus at the beginning of each of your turns.
At your option, a water vehicle you ride gains resistance to bludgeoning, lightning, piercing, slashing, and thunder damage. You also gain advantage on Perception and Insight checks to detect threats to the vehicle or its occupants. Spells you cast that restore hit points can also target the vehicle to repair damage, even if the vehicle would not normally be a valid target for the spell.
Also at 10th level, you bring the power of the sea along with you wherever you go. Whenever you take the Dash action, your movement speed increases by 10 feet and you summon an enormous wave of water that crashes over the area around you (if you are underwater, you instead create a powerful current around you with the same effects). All non-magical flames within 5 feet of your path are immediately extinguished, and creatures you become adjacent to while dashing must make a Strength saving throw against your spell save DC or be pushed 10 feet away from you. Your Tidal Surge activates automatically, but you may suppress it if you wish (no action required).
At level 14, you can transform yourself into a powerful denizen of the depths. When you use Wild Shape, you can instead spend 2 uses to transform into a plesiosaur, or 4 uses to transform into a young river dragon. At level 20, when you use Wild Shape you can spend 6 uses to transform into an adult river dragon.