Devouring Heart

Once a minor god of feasts, the Devouring Heart was never very important or powerful. It lived in the shadow of its greater kin, forced to serve them in hallow halls or hellish banquets. When free of those obligations, it roamed Khalaan, taking part in feast holidays, festivals, and good cheer in equal part. Across the centuries, it became a gourmand and had tasted everything there was to eat, from boiled bark to royal extravagance. Its divine existence was good, and would remain so until a powerful spirit challenged it for its mantle of divinity.
The Devouring Heart won the contest and killed the spirit with a bite that severed it in half - as soon as it had done so, new power surged through its body. The challenger was soon cooked and eaten in whole, and the Devouring Heart found the taste that would define its existence from now on. Once cheerful and gregarious, the Devouring Heart became withdrawn and secretive. It hunted minor spirits and consumed them to increase its power and whet its now unstoppable appetites for divine flesh. Even if it wanted to, it could not stop.
This hunger would in time lead to the Great Consumption, a war across generations, where spirits and gods were consumed in secret and then in the open. The world changed, as divine aspects merged and digested together inside the god now known as the Devouring Heart. After consuming the limits of the world, it was filled with terrible clarity of its deeds. To prevent itself from dooming everything and everyone, it turned its hunger on itself and fell into a deep, self-cannibalizing slumber.
Today, the Devouring Heart hovers in the skies above Khalaan, replacing the moon it once consumed. A vaguely humanoid lump of flesh, hair, teeth, and bone, it's surrounded by floating temples and towers.

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Warlocks can chose the Devouring Heart as their Patron.
The Devouring Heart
Your patron is the Devouring Heart, an all-consuming deity that devoured the pantheon and reshaped reality. You share its hunger and gain the ability to consume others for power.
The Devouring Heart is a silent patron, making its wishes known through urge and instinct. It's directives are simple - the Warlock must consume enough or perhaps specific things to keep the Heart, if not sated, then at least temporarily quiet.
Expanded Spell List
The Devouring Heart 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	Absorb Element, False Life
2nd	Ray of Enfeeblement, Enhance Ability
3rd	Vampiric touch, Hunger of Hadar
4th	Banishment, Sickening Radiance
5th	Enervation, Contagion

Consume
At 1st level, you gain the ability to consume the essence of fallen enemies. When a creature dies within touch range of you, you can use your reaction to consume its essence. You recover one expended Hit Die.
You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.
Digest
Also at 1st level, you can rapidly process the essence you've consumed to fuel your abilities. As an action, you can expend up to a number of Hit Dice equal to your proficiency bonus. For each Hit Die expended, roll the die and add your Constitution modifier. You regain hit points equal to the total.
You can use this feature twice per short rest. Each use can expend up to your proficiency bonus in Hit Dice.
Gnaw
Starting at 6th level, your attacks hunger for your enemies flesh. When you hit a creature with an attack, you can expend one Hit Die to deal extra necrotic damage to the target. Roll the Hit Die and add your Charisma modifier; the target takes that much extra necrotic damage.
You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.
Devour Magic
At 10th level, you gain the ability to consume parts of yourself to replenish your spell slots. As an action, you can expend any number of Hit Dice to recover expended spell slots. The spell slots can have a combined level that is equal to or less than half the number of Hit Dice expended (rounded down).
For example, expending 4 Hit Dice could recover two 1st-level spell slots, one 2nd-level spell slot, or one 1st-level and one 2nd-level spell slot. Once you use this feature, you can't use it again until you finish a long rest.
Voracious Consumption
At 14th level, your connection to the Devouring Heart reaches its pinnacle, allowing you to consume essence on a massive scale. Once per long rest, as an action, you can unleash your patron's insatiable hunger in a 30-foot radius centered on you. Each creature of your choice in that area must make a Constitution saving throw against your warlock spell save DC.
On a failed save, a creature takes 8d8 necrotic damage and you regain hit points equal to half the total damage dealt to all creatures. For each creature that fails the save, you also regain one expended Hit Die.
On a successful save, a creature takes half damage, and you don't regain hit points or Hit Dice from that creature. After using this feature, you can immediately use your Digest feature as a bonus action without expending any Hit Dice, instead rolling a number of d6s equal to your proficiency bonus and regaining that many hit points.