Upon consuming dragon hearts it has granted you a communion with dragons, not any dragon in particular, not even Tiamat or Buhamut are your patrons.  you are not devotion to a deity but rather the Dragon Communion magic derives purely from the draconic essence within the hearts.

Expanded Spell List

The following spells are added to the warlock spell list for you and they are always prepared.

Draconic Communion Expanded Spells

 

Spell Level	Spells
Cantrips	Elementalism, Sorcerous Burst
1st	Chromatic Orb, Hunter's Mark
2nd	Dragon's Breath, Flame Blade
3rd	Spirit Guardians, Call Lightning
4th	Conjure Minor Elementals, Wall of Fire
5th	Summon Dragon, Flame Strike

 

Additionally You may cast spells from the expanded spell list by spending draconic communion charges equal to the spell level instead of expending the appropriate spell slot spell slot. If done this way the spell is in it's base form and cannot be up cast,

Draconic Communion

You gain a number of Draconic Communion charges equal you your Prof.+Warlock level, that recharge over a short rest. In addition you may have your spells do lightning damage instead of the normal damage.

Craggy Scales

You gain a natural armor that is equal to 10+Dex+Cha as long as you aren't wearing any armor or wielding a shield as well as resistance to lightning damage

Draconic Vistage

Starting at 6th level, you gain additional uses for your Draconic communion charges these abilities are treated as spells and are affected by effects like anti-magic fields and for purposes of the spell level, like counterspell, the spell levels are equal to the amount of draconic communion charges used. You are unaffected by any difficult terrain created by these abilities and you take no damage from these abilities. Using these abilities don't take somatic nor verbal components 

The following abilities cost 3 Draconic communion charges per use:

Draconic Transformation

Casting Time: 1 bonus action
Range: Self
Duration: 1 minute

You channel the might of a dragon, transforming your body with draconic features. Until the ability ends, you gain the following benefits:

• Draconic Wings. You sprout wings, granting you a flying speed of 40 feet. As well as your size increasing one size category

• Eye of the Storm. For the duration of this ability the area within a 30 feet radius of you is difficult terrain for everyone except you.

• Thunderous Breath. As an action on each of your turns, you can exhale a 45-foot cone of lightning. Each creature in the area must make a Dexterity saving throw against your spell save DC, taking 3d12 lightning damage and pushed 15ft back on a failed save, or half as much damage and not being pushed on a successful save.

Dragon’s Thunderous Roar

Casting Time: 1 action
Range: 60 feet
Duration: Instantaneous

You unleash a thunderous roar infused with the power of a storm dragon, releasing a surge of lightning in a 30-foot cone. Each creature in the line must make a Dexterity saving throw. A creature takes 6d6 lightning damage and is pushed 10 feet away from you on a failed save, or half as much damage and no push on a successful save.

Additionally, the roar creates a booming echo. Until the end of your next turn, creatures within 10 feet of you have disadvantage on attack rolls against you due to the disorienting sound.

Draconic Volt Lance

Casting Time: 1 action
Range: 90 feet
Duration: Instantaneous

You conjure a spear of lightning infused with draconic ferocity and hurl it at a creature you can see within range. The target must make a Dexterity saving throw, taking 6d8 lightning damage on a failed save, or half as much on a successful save. If the target fails the save, you can immediately teleport up to 30 feet to an unoccupied space you can see, as residual lightning energy propels you with dragon-like speed.

The following are unlocked at 7th level and cost 4 draconic Communion charges:

Storm Dragon’s Wrath

Casting Time: 1 action
Range: 120 feet
Duration: Concentration, up to 1 minute

You summon the fury of a storm dragon, creating a 20-foot-radius sphere of crackling lightning centered on a point you choose within range. The sphere is difficult terrain. Each hostile creature in the sphere when it appears, or that ends its turn there, must make a Dexterity saving throw. A creature takes 4d8 lightning damage on a failed save, or half as much on a successful save.

As a bonus action on each of your turns, you can call down a bolt of lightning from the sphere to strike one creature within 30 feet of the sphere’s center. The target must make a Dexterity saving throw, taking 2d8 lightning damage on a failed save, or half as much on a successful save.

 

Draconic Skyfang

Casting Time: 1 action
Range: 120 feet
Duration: Instantaneous

You summon a jagged bolt of draconic lightning that strikes a creature you can see within range, shaped like the fangs of a storm dragon. The target must make a Dexterity saving throw, taking 7d8 lightning damage on a failed save, or half as much on a successful save. If the target fails the save, it is marked by a crackling draconic sigil until the end of your next turn. While marked, the target emits dim light in a 10-foot radius, and the next attack roll against it has advantage as the sigil guides the strike.

Draconic Thunderclaws

Casting Time: 1 action
Range: Self
Duration: 1 minute

You infuse your body with the electrified might of a storm dragon, causing your hands to crackle with lightning shaped like draconic claws. You gain the following benefits:

• Thunderclaw Strike. When you use this ability, and as an action on each of your subsequent turns, you can make up to two Thunderclaw strikes against creatures within 5 feet of you. On a hit, the target takes 4d8 lightning damage, and you can push it 10 feet away from you. 

• Electrified Prowess. Your melee weapon attacks and spell attacks deal an additional 1d8 lightning damage (included in the Thunderclaw Strike).

The following are unlocked at 9th level and cost 5 draconic Communion charges:

Draconic Stormcall

Casting Time: 1 action
Range: 120 feet
Duration: Concentration, up to 1 minute

You summon a roaring storm infused with draconic lightning, centered on a point you can see within range, forming a 20-foot-radius, 40-foot-high cylinder. The storm is difficult terrain and emits dim light in a 20-foot radius. When a creature enters the storm for the first time on a turn or starts its turn there, it must make a Dexterity saving throw, taking 5d10 lightning damage on a failed save, or half as much on a successful save.

As a bonus action on your turn, you can move the storm up to 30 feet to a point you can see within range. Additionally, while you are within the storm, you gain a flying speed of 60 feet as draconic lightning surges through you, and you can hover.

Draconic Lightning Fang

Casting Time: 1 action
Range: 150 feet
Duration: Instantaneous

You conjure a massive bolt of lightning shaped like a dragon’s fang, striking a creature you can see within range. The target must make a Dexterity saving throw, taking 8d10 lightning damage on a failed save, or half as much on a successful save. If the target fails the save, you channel the dragon’s ferocity: until the end of your next turn, your spell attacks deal an additional 2d10 lightning damage as residual draconic energy surges through you.

Greater Draconic Transformation

Casting Time: 1 bonus action
Range: Self
Duration: 1 minute

You channel the formidable essence of a storm dragon, transforming your body with enhanced draconic features.You gain the following benefits:

• Stormflight Wings. You sprout powerful wings, granting you a flying speed of 60 feet and the ability to hover. As well as your size category increasing by one size.

• Draconic Fortitude. Your skin hardens with shimmering scales, granting you resistance to slashing, piercing, bludgeoning and lightning damage and a +2 bonus to AC.

• Thunderous Breath. As an action on each of your turns, you can exhale a 60-foot cone of lightning. Each creature in the area must make a Dexterity saving throw against your spell save DC, taking 6d12 lightning damage and being pushed back 45ft on a failed save, or half as much and not pushed on a successful save.

The following are unlocked at 11th level and cost 6 draconic Communion charges:

Dragon’s Storm Barrage

Casting Time: 1 action
Range: 120 feet
Duration: Instantaneous

You summon the wrath of a storm dragon, unleashing a barrage of four lightning bolts that strike up to four creatures you can see within range. For each bolt, make a ranged spell attack against a target. On a hit, the target takes 4d10 lightning damage, and it must succeed on a Wisdom saving throw against your spell save DC or be frightened of you until the end of its next turn, overwhelmed by the draconic fury. On a miss, the target takes no damage and is not frightened. You can direct multiple bolts at the same target, and if a target is hit by more than one bolt, it has disadvantage on the Wisdom saving throw.

Dragon’s Crescent Storm

Casting Time: 1 action
Range: Self (60-foot cone)
Duration: Instantaneous

You channel the primal might of a storm dragon, unleashing a crescent-shaped wave of lightning in a 60-foot cone. Each creature in the area must make a Strength saving throw. On a failed save, a creature takes 10d8 lightning damage, is knocked prone, and is pushed 10 feet away from you. On a successful save, it takes half as much damage and is neither knocked prone nor pushed. The wave’s draconic energy crackles with such intensity that creatures that fail the save have disadvantage on their next attack roll or ability check before the end of their next turn.

The following are unlocked at 13th level and cost 7 draconic Communion charges:

Dragon’s Apocalyptic Tempest

Casting Time: 1 action
Range: 120 feet
Duration: Instantaneous

You invoke the cataclysmic wrath of a storm dragon, summoning a 30-foot-radius, 60-foot-high tempest of lightning centered on a point you can see within range. Each creature in the area must make a Dexterity saving throw. On a failed save, a creature takes 12d8 lightning damage and is marked by draconic energy for 1 minute; on a successful save, it takes half as much damage and is not marked. A marked creature has vulnerability to lightning damage and emits dim light in a 5-foot radius. A creature can repeat the saving throw at the end of each of its turns, ending the mark on a success.

 

Draconic Storm Ascendancy

Casting Time: 1 action
Range: Self
Duration: 1 minute

You transform into a storm dragon avatar, wreathed in crackling lightning, embodying the apocalyptic might of a dragon. You gain the following benefits:

• Draconic Form: Your size becomes one size larger, you grow wings granting a flying speed of 60 feet, and your AC increases by 2. You are immune to lightning and thunder damage.

• Storm Claws: Your draconic communion abilities do 4d8 lightning damage in addition to their original damage addition when a creature is hit by a draconic communion ability they must make a Strength saving throw, on top of any other saves and effects, or be knocked prone

• Lightning Breath: As an action, you can exhale a 60-foot cone of lightning. Each creature in the area must make a Dexterity saving throw, taking 8d10 lightning damage on a failed save, or half as much on a successful save. You can use this breath weapon once during this duration.

• Storm Aura: At the start of each of your turns, creatures of your choice within 20 feet of you take 2d10 lightning damage, as arcs of electricity lash out.

When you us this ability, you immediately unleash a surge of lightning in a 30-foot radius centered on yourself. Each creature in the area other than you must make a Dexterity saving throw, taking 6d10 lightning damage on a failed save, or half as much on a successful save.

The following are unlocked at 15th level and cost 8 draconic Communion charges:

Dragon’s Cataclysmic Onslaught

Casting Time: 1 action
Range: 120 feet
Duration: Instantaneous

You channel the apocalyptic might of a storm dragon, unleashing six searing bolts of lightning that strike up to six creatures you can see within range. For each bolt, make a ranged spell attack against a target. On a hit, the target takes 6d10 lightning damage and must succeed on a Wisdom saving throw against your spell save DC or be frightened for 1 minute, cowering before the draconic wrath. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on a success. On a miss, the target takes no damage and is not frightened. You can direct multiple bolts at the same target, and if a target is hit by more than one bolt, it has disadvantage on the Wisdom saving throw.

Dragon’s Apocalyptic Surge

Casting Time: 1 action
Range: 150 feet
Duration: Instantaneous

You summon the cataclysmic wrath of a storm dragon, causing a 40-foot-radius sphere of lightning to erupt from a point you can see within range. Each creature in the area must make a Constitution saving throw. On a failed save, a creature takes 14d8 lightning damage and is paralyzed for 1 minute, overwhelmed by the draconic energy. On a successful save, it takes half as much damage and is not paralyzed. A paralyzed creature can repeat the saving throw at the end of each of its turns, ending the effect on a success. The surge’s intensity leaves the ground scorched, creating difficult terrain in the area for 1 minute.

The following are unlocked at 17th level and cost 9 draconic Communion charges:

Dragon’s Celestial Cataclysm

Casting Time: 1 action
Range: 1 mile
Duration: Instantaneous

You invoke the ultimate wrath of a storm dragon, summoning a cataclysmic storm of lightning that ravages a 60-foot-radius sphere centered on a point you can see within range. Each creature in the area must make a Dexterity saving throw. On a failed save, a creature takes 16d10 lightning damage and is banished to a stormy demiplane for 1 minute, wracked by draconic tempests. On a successful save, it takes half as much damage and is not banished. A banished creature is incapacitated and takes 2d10 lightning damage at the start of each of its turns. It can repeat the saving throw at the end of each of its turns, ending the banishment on a success and returning to the space it left or the nearest unoccupied space. The cataclysm’s energy scars the battlefield, creating difficult terrain in the area for 1 hour.

Dragon’s Annihilating Cascade

Casting Time: 1 action
Range: 150 feet
Duration: Instantaneous

You channel the obliterating might of a storm dragon, unleashing ten searing bolts of lightning that strike up to ten creatures you can see within range. For each bolt, make a ranged spell attack against a target. On a hit, the target takes 10d12 lightning damage and must succeed on a Dexterity saving throw against your spell save DC or begin to disintegrate, taking 4d12 lightning damage at the start of each of its turns for 1 minute. A disintegrating creature can repeat the saving throw at the end of each of its turns, ending the effect on a success. If this ongoing damage reduces a creature to 0 hit points, it is reduced to ash, leaving no remains. On a miss, the target takes no damage and is not affected by the disintegration. You can direct multiple bolts at the same target, and if a target is hit by more than one bolt, it has disadvantage on the Dexterity saving throw. The cascade’s energy fractures the ground, creating difficult terrain in a 60-foot radius centered on you for 1 hour.

Near Peak Draconic Prowess

At 10th level, your Draconic Communion grows near it's peak.

As an action, you channel the might of your draconic patron, embracing the ancient power of a storm dragon. For 1 minute, you gain the following benefits:

• Draconic Skin:  +1 AC bonus when not wearing armor.

• Thunder Step: Allows teleportation up to 60 feet as a bonus action, with creatures within 15 feet of where you teleport to take 3d10 lightning damage and are pushed 15 feet back.

• Empowered Spells: When you cast a spell that deals lightning damage, it deals an additional 2d8 lightning damage.

• Storm's Fury: At the end of each of your turns, each hostile creature within 20 feet of you takes 1d6 lightning damage, and you gain temporary hit points equal to the total damage dealt this way. Any temporary hit points gained from this ability stack but are lost at the end of this duration.

You may use this ability a number of times per long rest equal to your proficiency bonus.

True Dragon

Starting at 14th level, you can shapeshift into a Adult Brass Dragon. However the dragon's breath weapons are replaced by a 60-foot cone that deals 10d10 lightning damage on a failed Dex save and stuns, on a success they take half and are not stunned (It recharges on 5-6). The DC uses your Charisma stat instead of the dragons. You cannot use the dragons legendary actions of the dragon either. This transformation lasts for 1 hour.

While you are transformed, the following rules apply:

• The Dragon's AC is equal to your own
• Your game statistics are replaced by the statistics of the dragon, but you retain your alignment, personality, and Intelligence, Wisdom, and Charisma scores. You also retain all of your skill and saving throw proficiencies, in addition to gaining those of the creature. If the creature has the same proficiency as you and the bonus in its stat block is higher than yours, use the dragon's bonus instead of yours. You may use the dragon's legendary resistances but not legendary actions.

• When you transform, you assume the dragon's hit points and Hit Dice. When you revert to your normal form, you return to the number of hit points you had before you transformed. However, if you revert as a result of dropping to 0 hit points, any excess damage carries over to your normal form, For example, if you take 10 damage in animal form and have only 1 hit point left, you revert and take 9 damage. As long as the excess damage doesn't reduce your normal form to 0 hit points, you aren't knocked unconscious.

• You retain the benefit of any features from your class, race, or other source and can use them if the new form. However, you can't use any of your special senses, such as darkvision, unless your new form also has that sense.

• Your equipment merges into your new form.