Deep Sea

 Deep Sea Sorcerers are respected or feared by coastal townsfolk depending on what stories they hear. Some may get mistaken with Sea Hags.

Deep Sea Spells

You can cast the Shape Water cantrip at will. You learn additional spells when you reach certain levels in this class, as shown on the Deep Sea Spells table. Each of these spells counts as a sorcerer spell for you, but it doesn’t count against the number of sorcerer spells you know.

You cannot replace these spells when you gain a sorcerer level.

Aquatic Affinity

Starting at Level 1, you can breathe underwater, and your swimming speed is equal to your movement speed. 

Also, whenever you are in water that is at least ankle deep, you get +2 to your AC.

Tidal Casting

Starting at Level 6, you can use sorcery points to cast the spell at a higher level.
The spell should be 4th-level or below and you can only upcast spells up to 6th-level. You use one sorcery point for each level of upcasting. You use the original spell slot for the spell.

Aquatic Form

When you are hit by an attack or fail a dexterity or strength saving throw, you can use your reaction to change into an aquatic form until the end of your next turn. If you were going to take damage from the triggering attack/effect, you take no damage.
While you are in this form you are immune to slashing, bludgeoning and piercing damage from nonmagical attacks. You have resistance to fire damage. You cannot be grappled, paralyzed, poisoned, restrained or stunned.
At the end of your next turn, you go back to your original form and you are knocked prone.
Once you use this feature, you can’t use it again until you take short a rest.

One with the Ocean

At 18th level you become adept at using your aquatic form.
Starting from this level, you gain resistance to slashing, bludgeoning and piercing damage from nonmagical attacks.
Your swimming speed is twice time your movement speed.
You have advantage on saving throws while you are underwater.
Additionally, once per long rest, you can cast spells from your Deep Sea Spell List without expanding a spell slot and without needing material components.