Herald of Hadar

In your desperation for the power, you have made a pact with Hadar the Dark Hungerer. The pact hast transformed your body and soul. Your eyes have turned pitch black,  you grow tendrils of darkness out of your armour, and when you speak your voice is mutated, sounding like an echo.

The power has come with a great price, you have no need for substance, you cannot sleep, but you feel constant hunger. Deep unending hunger of Hadar. Clinging to your life like the Dark Hungerer itself. Your off hands turn black as darkness, and you use it to devour living things around you. Each day you slowly seep the life force from living things around you unless you devour a creature. with your corrupted hand. You can spend one-hour channelling the dark force from your black hand into the corpse, devouring it.

Hadar the Dark Hungerer is linked to your soul rendering you immune to disease and you no longer feel the passage of time. Days, Months, Years, are all the same to you. Everything feels like it happened in the distant past. Sometimes you even remember things from creatures you have devoured, mistaking them for yours.

Years have passed and your body hardened by the devourer's influence, turning your skin greyish and harder to penetrate. You have become proficient with martial weapons but you do not remember when did you learn it. You are proficient with the martial weapon as long as your corrupted hand is touching it.

Breath of a Dying Star

Starting at 1st level, once per short rest, as an action, you summon a cloud of darkness that explodes around you in all directions. Creatures touched by the darkness take 1d8 necrotic damage and can't regain hit points as long as they are in 30 feet reach of you or until dispelled.

This spell’s damage increases when you reach higher warlock levels. At 5th level, the damage is increased to 2d8 necrotic damage. Damage rolls increase by 1d8 at 11th level and 17th level.

Devouring Hand

At 1st level, your off hands turn black as darkness, and you use it to devour living things around you. Each day you seep the living force from anything around you, and every time a living creature dies nearby you must spend one hour channelling the darkness from your hand into the corpse until you completly devour it.

Your hand exists both in your realm and the real of Hadar, the Dark Hunger. The connection allow you to use your hand as a spellcasting focus.

Weapon of Darkness

Whenever you finish a long rest, you can spend one hour channelling the dark energy into that weapon. You must be proficient to use it and the weapon cannot have the two-handed property. With that weapon, you can use your CHA modifier for the attack and damage rolls until you finish your next long rest. 

Unnatural Armor

Starting at 1st level, while you are not wearing any armour, your Armor Class equals 10 + your Dexterity modifier + your Constitution modifier. You can not use a shield.

Hungerers veil

At 6th level, once per short rest, you can use your bonus action to activate Hungerers veil. Darkness seeps from you into the mortal realm, devouring heat. All creatures in ten feet radius take your charisma modifier as damage on each turn they stay in 10 feats of you.

Hungry Veil

As creatures around you fall to their death, you regen hit points equal to your charisma modifier. If you are on full health you cumulate temporary hit points up to your warlock level. 

Gate of Hadar

Starting at level 10, once per short rest you point at the location that you see in thirty feet range. You open a gateway to the dark between the stars, a region infested with unknown horrors. A 60-foot-radius sphere of blackness and bitter cold appears, centred on a point with range and lasting for the duration. This void is filled with a cacophony of soft whispers and slurping noises that can be heard up to 100 feet away. No light, magical or otherwise, can illuminate the area, and creatures fully within the area are blinded.

The void creates a warp in the fabric of space, and the area is difficult terrain. Any creature that starts its turn in the area takes 2d6 cold damage. Any creature that ends its turn in the area must succeed on a Dexterity saving throw or take 2d6 acid damage as milky, otherworldly tentacles rub against it.

Avatar of Hadar

At 14th level, if you are wearing no armour, your skin turns black, you lose your body hair and tentacles spawn from your body. Tentacles grab and touch any creature in 5 feet radius of you. Creatures that end their turn next to you must make DEX saving throw or take 1d6 acid damage.