Your patron is a mammoth sea creature of the depths.  You master is slowly preparing you so that you might server them more closely, more personally.  It is unclear why they have any interest in the goings on of surface dwellers but it is well documented that there are a number of peoples whom worship such creatures.  They are often reclusive island folk, and they also often have stories of those "blessed" by the deities whom were transformed and went to join them in the depths.

Extended Spell List

The Lurker in the Depths lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

Spell Level	Spells
1st	create or destroy water, fog cloud
2nd	alter self, moonbeam
3rd	tidal wave, wall of water
4th	control water, watery sphere
5th	dawn, maelstrom

Amphibious

You grow large noticeable gills on your neck or behind your ears, which enables you to breath water even while unconscious.  The skin between your fingers and toes stretches down like a web and your skin becomes slimy, this allows you to swim at a speed of 30 feet.  Your teeth come to a point and grow back quickly, you can use them to attack as a bonus action.  Your pupils grow larger and consume your irises, you gain darkvision to 60 feet.

Sea Spawn

At level 6 you transform into a Sea Spawn, you feel like this has been a long time coming.  Your skin grows scaly and turns blue/green/gray over your whole body, you grow fins along your length and appendages, and your eyes become bulbous.  Your darkvision extends to 120 feet, gain proficiency with trident and javelin, and are able to multiattack with your claw like nails.  However, you also must bathe yourself in salt water for 1 minute a day, each day that passes without doing this increases your level of exhaustion.

You are still considered a humanoid, but you are certainly not what you once were.  Though most people would regard you as a monstrosity, you are not considered one for purposes of targeting and detection.

Scion

Perhaps you always knew, but now at level 10 it is more readily apparent to all those that see you, the nature of that which you serve.

Dragon Turtle

Your skin grows tough and leathery, your limbs shorten and abdomen lengthens, you sprout a small tail, your teeth meld with your lips to form a beak, your nose and ears flatten leaving the holes more exposed, and your hands and feet are not just webbed your entire arms and legs are now flippers.  In this form your crawling speed is 20 feet, your swim speed is 40 feet, and you are always prone while on land.  You are able to polymorph into your previous, more humanoid, Sea Spawn form with the addition of a tail.

• You can attack with your tail as a bonus action for 1d4 bludgeoning damage, the target must make a Dexterity save or be knocked prone.
• Your AC increases by 1.

Kraken

Your skin thickens to form a chitinous shell, your jaw splits in the middle and each side form a mandible, all of your bones are now exterior, your hands form large pincers, and your legs split into sets of legs that come to a point without feet.  In this form you are only able to speak Aquan (a form of Primordial), but you are able to polymorph into your previous, more humanoid, Sea Spawn form with one pincer hand.

• When you multiattack, you can use your claws and/or your pincer for the two attacks.
• When you attack a target with your pincer, they must make a Dexterity save or be grappled by you.  You cannot use your pincer to attack any other targets while maintaining the grapple, however you can squeeze this target for 1d4+Strength as an attack so long as the grapple continues.
• You are Immune to disease and resistant to poison.

Leviathan

Your head grows soft and bulbous with feelers hanging from front, your body is sleek, all of your remaining bones are flexible, and your arms and legs are replaced with large tentacles.  In this form your walking speed is 20 feet, your swim speed is 40 feet, and you are able to polymorph into your previous, more humanoid, Sea Spawn form with one tentacle arm.

• You have advantage on melee attacks against creatures that have less than full health.
• When you multiattack, you can use your claws and/or your tentacle for the two attacks.
• Your Tentacles have a reach of 10 feet and do 1d6 Bludgeoning damage.

Defense Mechanism

At level 14 you may chose one of the three options below:

Ink Cloud

A 20- foot-radius cloud of ink extends all around you.  The area is heavily obscured for 1 minute, although a significant current/wind can disperse the ink.  Once per short rest you can release this cloud of ink as a bonus action or as a reaction to being the target of an attack, even if you took no damage.

Psychic Screech

You emit a terrible scream audible within 300 feet. Creatures within 30 feet of you must succeed on a Wisdom saving throw or be stunned until the end of your next turn. In water, the psychic screech also telepathically transmits your memories of the last 24 hours to your master, regardless of distance, so long as you and your master are in the same body of water.  You can perform this action once per short rest.

Steam Breath

You exhale scalding steam in a 15-foot cone.  Each creature in that area must make a Constitution saving throw, taking 2d6 fire damage on a failed save, or half as much damage on a successful one.  Being underwater doesn't grant resistance against this damage.  You can perform this action once per short rest.