Nadeko Snake Patrons

You have formed a pact with two Nadeko Snakes, serpentine apparitions that are invisible, and they have coiled around your body, protecting you, and casting spells in your stead, in return for sucking a sufficient amount of blood to keep them fed every day. Thankfully, this doesn't impede you, but the marks they leave on your body can still be quite painful.
The snakes get additional spells that they can cast:
1st- Absorb Elements, Ray of Sickness
2nd- Melf's Acid Arrows, Enhance Ability
3rd- Slow, Elemental Weapon
4th- Phantasmal Killer, Vitriolic Sphere
5th- Cloudkill, Contagion

Crushing Coils - Lvl1 Pact Feature

The snakes around your body help you in grappling creatures for you. You can use Charisma in place of Strength when you make an Athletics check to grapple.
When you successfully grapple a creature, and as a bonus action on subsequent turns while you have the creature grappled, you can force it to make a Constitution saving throw  against your spellcasting DC. On a fail, they take bludgeoning damage equal to an amount of d6s equal to half your warlock level, rounded up and can't cast spells with verbal components until the start of your next turn, halving that damage and ignoring the spellcasting penalty on a success.
The apparition snakes coiling around your body also protect you from harm. While you are not wearing any armor and not wielding a shield, your Armor Class equals 10 + your Dexterity modifier + your Charisma modifier. 

Starting from 14th level, you can use your bonus action to try and make the snakes coil around a creature grappled by you. To do so, make another grapple check. On a success, the target is restrained.

Corrosive Venom - Lvl6 Pact Feature

The Nadeko snakes tighten their grasp around your body to empower the spells they cast. You can spend hit die for the following effects:
Bypass Resistance: You can spend a hit die to bypass your enemy's resistance. When you deal acid or poison damage with a spell, the attack ignores the enemy's resistance.
Bypass Immunity: You can spend 2 hit dice to bypass your enemy's immunity. When you deal acid or poison damage with a spell, the attack ignores the enemy's immunity.
If you expend your last hit die with this feature, you gain a point of exhaustion.

Ophidic Affinity - Lvl 10 Pact Feature

Your snakes' constant biting has conditioned your body. You gain immunity to disease and poison, and resistance to acid damage.

Python Paragon - Lvl 14 Pact Feature

The apparitions coiling around you now extend to grapple your enemies. Your snakes now count as hands for grappling, and can grapple creature to a range of up to 15ft. If grappling a creature with the snakes, your movement speed isnt impeded, so long as the creatures dont move out of range, at which point you have to drag them forward, which halves your speed. Using the spectral snakes you can also now grapple huge creatures.

Eldritch Invocation - Ophidian Override

Prerequisite: 5th level, Nadeko Snakes Patrons

When casting a spell, you can change it's damage type into poison or acid (your choice).