Maiden of the Mists

The Dead Mists of R’lyeh have for eons been a deadly trap for astral travelers. Foolhardy wizards and mystics would push themselves further and further into the astral sea, and would eventually find themselves wrapped in the eldritch mists. Lost and without guide, they would inevitably succumb to the mist’s soul-draining effects, and would become little more than food for the astral beings who slept in the mists.
     Such was the fate of one such explorer: Faye Diamond, a scholar of the otherworldly from another time and another place. Lost in the mists, she assumed that her fate would be the same as those who had come before, and indeed it would have had she not made contact with The Master of the Mists. Though their astral connection, the Master taught her all that he could about how to navigate and control the mists, and though this intervention Faye was saved.
     Decades later, a much different woman returned to the mists which once threatened to consume her. Faye had become so attuned with the Dead Mists that they were now a part of her, and she a part of them. Fearing that she would finally be destroyed by the mists, she searched for her old master. Upon discovering his resting place and seeing his lifeless form on an eldritch golden throne, she immediately understood her final purpose: she would become the Maiden of the Mists, and would guide others the way her master had guided her years before.

The Dead Mists Expanded Spells 

Eldritch Investigation
Starting at 1st level, you learn to open your mind to the Dead Mists of R’lyeh, granting you eldritch insights and power. As a bonus action, you can deal yourself necrotic damage equal to 1d8 times the level of your Pact Magic slots. At the start of your next turn, you regain an expended Pact Magic slot.
     Damage from this ability ignores both damage resistance and damage immunity, and does not subtract from your temporary hit points, if you have any. If this ability reduces you to 0 hit points, you are knocked unconscious, even if you have temporary hit points. You must be able to perform the somatic components of a spell in order to use this ability.

Mist-Fueled Recovery
Starting at 6th level, your body begins to merge with the Dead Mists, allowing you to heal your mortal form by burning eldritch energy. As an action on your turn, you can consume one of your available Pact Magic spell slots; doing so heals you 1d8 hp per spell level of the slot consumed.

Mist Form
At 10th level, you learn to fully immerse yourself in the Dead Mists, transforming you in to a hazy, misty reflection of your true self. As an action, you can cast the spell gaseous form on yourself without using a spell slot.

Master of the Mists
At 14th level, you learn to infuse the Mists of R’lyeh into your spells, leeching vitality from your foes. Once per turn, when you deal necrotic damage to a hostile creature with a warlock spell, you regain hit points equal to 1d8 + your Charisma modifier.

New Spells

These spells are available to a warlock of the Dead Mists.

Heedless Lash
1st-level conjuration
Casting Time: 1 action
Range: 120 feet
Components: V, S
Duration: Instantaneous
You conjure forth a glowing, white tendril formed of the Dead Mists of R’lyeh, which lashes out at a foe, but also wracks you with pain. Make a ranged spell attack roll against a creature within range; if you hit, the target takes 4d8 necrotic damage. You take 1d8 necrotic damage when you cast this spell. This damage ignores both damage resistance and damage immunity.
     At Higher Levels: If you cast this spell using a slot of 2nd level or higher, the damage to your target increases by 2d8 and the damage to yourself increases by 1d8 for each slot level above 1st.

Mists of Time
9th-level transmutation
Casting Time: 1 action
Range: Self
Components: V, S
Duration: Instantaneous
You throw caution to the wind and wrap yourself in the Mists of R’leyh, imposing a shadow of the past on your mind and body. You regain 4 spell slots of 5th level or lower.
     When you cast this spell, you can choose drink deep the Dead Mists and take necrotic damage equal to half your current hit points. This damage ignores both damage resistance and damage immunity. If you do so, you regain the expended uses of up to three abilities which normally recover when you take a rest.
     Once you cast this spell, you cannot cast this spell again for 24 hours, even if you have an available 9th level spell slot.

Mistbound
2nd-level conjuration
Casting Time: 1 action
Range: Self (20-foot radius)
Components: V, S
Duration: Concentration, up to 1 minute
When you cast this spell, glowing white tendrils of smoke reach up from the ground in a 20-foot radius area around the point where you stand. When a creature other than you enters the affected area for the first time on a turn or starts its turn there, the creature must succeed on a Dexterity saving throw or be grappled by the tentacles until the spell ends. A creature other than you that starts its turn in the area and is already grappled by the tentacles can make a Strength or Dexterity check (its choice) against your spell save DC. On a failure, it can’t take actions or reactions until the start of its next turn. On a success, it frees itself.
     When you cast this spell, you take 2d8 necrotic damage, and you take an additional 1d8 necrotic damage at the end of each round you concentrate on it. This damage ignores both damage resistance and damage immunity.

Oblivion
5th-level conjuration
Casting Time: 1 action
Range: Self (40 foot radius)
Components: V, S
Duration: Instantaneous
You open an instantaneous portal to the heart of R’lyeh, allowing the Dead Mists to wreak havoc. Each creature within a 40-foot radius area around you (including yourself) must make a Dexterity saving throw. A target takes 6d8 necrotic and 6d8 bludgeoning damage on a failed, or half as much on a successful one.
     When you cast this spell, you can choose to take 10 points of necrotic damage, which ignores both damage resistance and damage immunity. If you do so, you can choose a number of creatures in the area equal to your spellcasting modifier. The chosen creatures automatically succeed on the saving throw against this spell.

Scouring Mists
3rd-level conjuration
Casting Time: 1 action
Range: 120 feet
Components: V, S, M (a handful of white phosphorous)
Duration: Instantaneous
With a gesture, you fling 4 waves of the Dead Mist at targets within range, rending their flesh from their bones. You may fire them at one target or several. A target must make a Dexterity saving throw for each wave they are targeted with. A target takes 3d6 necrotic damage on a failed save, and half as much on a successful one.
     When you cast this spell, you take 1d8 necrotic damage for each wave you launch. This damage ignores damage resistance and damage immunity.
     At Higher Levels: If you cast this spell using a spell slot of 4th level or higher, you can fling an additional wave per slot level above 3rd.

Magic Items

Amulet of the Elder Gods
Wondrous item, legendary (requires attunement by a sorcerer, wizard, or warlock)
This simple bronze disc, held in place by a green silken sash and carved with the Elder Symbol, radiates incredible abjurative power. The amulet has 3 charges. When you would take damage from any source, you can use your reaction and expend 1 charge to instead take no damage. You then make a ranged spell attack targeting a creature you can see within 120 feet. On a hit, that creature takes necrotic damage equal to the damage you would have taken.
     The amulet regains 1d3 expended charges daily at dawn.

Elder Ring
Ring, very rare (requires attunement by a sorcerer, wizard, or warlock)
This ornately carved gold ring is scrawled with eldritch sigils and runes, and has wide, flat engraving of the Elder Symbol on its top. While attuned to the ring, you add +2 to your spell attack rolls and save DCs. Additionally, when you deal damage with a spell, you can add 1d6 necrotic damage to the damage roll.

Starshield Necklace
Wondrous item, very rare (requires attunement by a spellcaster)
This lavish golden necklace take the shape of a large golden disc, studded with numerous gemstones, with a massive ruby as its central setting. While attuned to the starshield necklace, you can use a bonus action to consume a spell slot and regain 1d8 hit points for each level of the slot consumed.

Changelog: 12/5/16: Spells: Spells which deal damage to yourself are clarified to deal unavoidable, irreducible damage
Changelog: 12/5/16: Spells deal damage which ignores damage resistance and immunity.
Mists of time changed
Master of Mists: changed to only affect hostile creatures.
Eldritch Investigation: changed to ignore Temp HP, and require somatic components.
Scouring Mists: damage reduced to 3d6 per blast