The Black Greatwyrm

Black Greatwyrms are some of the most ancient, powerful, and malevolent mortal beings in all of Toril.  By the time a Black Dragon reaches the Greatwyrm status of its life, it has immense sorcerous power, and many Dragons supplement their innate Draconic magic with Necromantic wizardry and fell energies drawn from the Plane of Shadow.  Black Dragons are wholly evil creatures who revel in the suffering of others.  They love to torture and torment their enemies, giving them hope they can escape only to crush it again.  They hate to see others succeed and prosper and live to bring misery and suffering into the world.  While other Chromatic Dragons may fly from their lairs to swoop down onto a small village or town near its lair that has flourished in some way to raise its ire, Black Dragons are much more cautious, preferring to ambush or trap their pray.  They know even their immense physical might and magical power cannot stand up against armies of spellcasters and siege weapons.  Black Greatwyrms will, on occasion, employ agents to help them bring about ruin and decay to the larger world.

These agents are empowered with a portion of the Black Greatwyrm’s immense magical power, rewarding them with the abilities of a Warlock in exchange for helping the Black Greatwyrm bring decay and ruin to all that thrives.  A warlock that makes a pact with a Black Greatwyrm must be very cautious to always please their master, as Black Dragons are notoriously fickle and sadistic.  If their slave is not enriching their hoard or helping to bring about the destruction of nearby cities and towns, then the Black Dragon will slay them and let their corpse rot before consuming it.  With a Black Greatwyrm patron, every day could be your last.

Black Dragons also hate and mistrust all other dragons, and they are constantly on the lookout for other Dragons encroaching on their territory.  To this end, they employ wards and divination magic to spy on their enemies and alert them when their territory has been breached.  A Black Dragon will sometimes send Warlocks in its service out to slay other Dragons it feels are a threat to it.

The alignment of nearly all Warlocks that make a Pact with the Black Great Wyrm are going to be Chaotic Evil to match their master's malevolent, sadistic nature.  Black Dragons that cast off the influence of Tiamat and lean towards goodness or even neutrality are extraordinarily, minutely, indiscernibly rare.  While the other Chromatic Dragons can overcome their villainous nature, Black Dragons simply revel in death too much.  However, just because your Patron is a malevolent maniac that wants the world to rot away does not mean you have to be. 

Some Warlocks that draw their power from a Chromatic Dragon secretly work to subvert and eventually destroy their masters.  Great Wyrms are some of the most powerful creatures on the Material Plane, but they are still mortal, and therefore they can be killed.  However, a Warlock that kills its Draconic patron will lose their magical ability, so many will prepare an Imprisonment spell to trap their Patron's soul to keep their magical powers.

The magic learned from these nefarious creatures focuses on damage enemies with acid and decay and debilitating them with disease and weakness.  Insects, spiders and other vermin infest the land near a Black Dragon's lair, and you have learned to manifest their powers and summon them to assist them in combat.

Expanded Spell List

The Black Greatwyrm lets you choose from an expanded list of spells when you learn a warlock spell.  You also gain the Acid Splash cantrip.  It does not count against the total number of cantrips you know. The following spells are added to the warlock spell list for you.

Black Greatwyrm Expanded Spells

Draconic Enhancement

Starting at first level, your patron infuses you with some of their Draconic essence.  You learn to speak, read, and write Draconic.  You gain resistance to Acid damage.  You gain Darkvision out to 60 feet.  If you already have Darkvision, it's range is increased by 30 feet.  You can see in dim light within the radius as if it were bright light, and in darkness as if it were dim light. You can't discern color in darkness, only shades of gray. 

Amphibious Ambusher

Black Dragons are the least physically adept of the Chromatic Dragons.  Their slender, almost gaunt frames give them surprising dexterity for such large creatures.  Combined with their amphibious nature, and Black Dragons are perhaps the best ambush predators in all of Toril.  They hide beneath the brackish swamp, using their blindsight to know when to attack to devastating effect.

Beginning at 6th level, you are now also a master of the ambush.  You gain the ability to breathe underwater, you gain a swimming speed of 30 feet, and, while submerged beneath water, you can hide as a bonus action on your turn.  Additionally while hidden or invisible, any time you critically hit an enemy, you can roll one additional damage die when determining the extra damage.

Noxious Constitution

The lairs of Black Dragons are choked with the overpowering odor of rot and decay, and indeed, Black Dragons prefer to let their food begin to decompose before the consume it.  The swamplands around their lairs are filled with poisonous waters, sulfur-choked rivers, and ponds filled with decomposing animals.

Beginning at tenth level, your patron grants you the ability to move through their territories unhindered.  You gain resistance to poison and necrotic damage.  You can eat or drink pretty much anything organic without suffering any negative effects, be it the poisonous leaves of an aconite plant or a rotting beast that has been decomposing for a month.  You can drink water from sources filled with toxins or parasites, corrupted with sulfur, or filled with dead animals. You cannot be poisoned by anything that you consume. Additionally, you automatically succeed on saving throws that leave you poisoned or incapacitated due to an overpowering odor, like the spell Stinking Cloud or a Troglodyte's stench.

Machinations of the Unliving

Black Dragons are obsessed with death, and, as they grow older, some may begin to dabble with Necromantic magics, using their innate sorcerous abilities to further degrade their enemies by forcing them to serve them after death.  Whereas undead create by most Necromancers are abominable enough, Black Dragons create Zombies and Skeletons toughened against the decaying rot that suffusing their lairs, and completely immune to to dissolution power of their Acidic breath weapons.

Once you reach fourteenth level, you can as well.  You gain access to the spells Animate Dead and Create Undead.  They count as Warlock spells for you, but do not count against the number of Warlock spells that you know.  You can cast Animate Dead a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.  You can cast Create Undead once, and must finish a long rest to use it again.  In addition, undead created by your spells are immune to acid damage and, if they are not already, resistant to necrotic damage.