Curse of Leviathan

These sorcerers were not born with natural magic, but they were cursed by the Leviathan, a legendary sea creature. This can happen either because the Leviathan had a bad day, or because they somehow pissed him off enough to curse them. Anyone with this curse slowly takes on the Leviathan's natural abilities and looks more and more like a humanoid Leviathan, they will start to grow tails and their legs will become webbed making them be able to swim faster, but they always need lots of water otherwise they will start to get weaker and weaker as long as they keep getting more dehydrated. They are also weak to fire and lightning damage and they have a resistance to water. This curse is inherited with the family bloodline.

Leviathan Features

At 1st level, you gain Leviathan-like attributes and the ability to swim fast, increasing your swimming speed by 10 ft.
You can speak, read, and write Draconic.

Leviathan Resilience

Additionally, parts of your skin are covered by a thin sheen of dragon-like scales. When you aren’t wearing armor, your AC equals 13 + your Strenght modifier.

As magic flows through your body, the physical features of your curse become visible. At 1st level, your hit point maximum increases by 2 and increases by 2 each time you gain a level in that class.

Steam Breath

Starting at 6th level, you learn the ability Steam Breath (Recharge 2-3). the user exhales a stream of hot steam in a 45-foot cone. Each creature in the area must make a DC 17 Dexterity saving throw, taking  (4d6) cold damage and (4d6) fire damage on a failed save, or half as much on a successful one.

Frightful Presence.

Frightful Presence.
At 9th level, you gain the ability to use Frightful Presence. Any creature of the user's choice that is within 50 feet of the user and senses him must succeed on a DC 18 Wisdom saving throw or become frightened for 3 minutes. A creature can repeat the saving throw at the end of each turn, ending the effect on success for itself. If a creature's saving throw succeeds or the effect ends for it, the creature is immune to Frightful Presence for 24 hours.

Leviathan Body

When you enter the water, your body completely transforms into a large Leviathan but only if you choose to transform, and you gain +2 to your Dexterity and +1 to your Strength underwater. After you leave the water, you transform back to your original state within the next 20 minutes, and until then your movement speed on land is reduced from 30 feet to 20 feet.