An Ancient Red Dragon is one of the most ancient, powerful, and fearsome mortal beings in all of Toril.  By the time a Red Dragon reaches the Great Wyrm status of its life, it has immense sorcerous power, and it is the epitome of the evil Dragon archetype.  "All Dragons are predators, but Reds are the most voracious, consuming far more than they require.  All Dragons are greedy, but Reds are avaricious beyond all point of reason, for they fully believe that all wealth belongs to those strong enough to take it.  And no amount of wealth is ever enough.  All Dragons are prideful, but Reds are arrogant in the extreme. They see themselves as the pinnacle of Draconic perfection."  This perfectly describes Red Dragons, the largest of the Chromatic Dragons and one of the most feared creatures in all the Multiverse.

Red Dragons crave to learn about the events in wider world but are territorial and isolationist in the extreme.  They fear to lose even a single coin from their hoards, so they rarely journey too far from their lairs.  To learn about the events of nearby kingdoms, the incursions of the Drow and Illithids from the Underdark, or, especially, the movements and actions of other Red Dragons, they enslave lesser beings to serve as agents, spies, and occasional assassins.  These agents are empowered with a portion of the Red Dragon's innate magical abilities, rewarding them with the abilities of a Warlock in exchange for helping them learn about events beyond their territories, enrich their hoards, and track down those who insult or steal from them.  A Red Dragon knows the location of every single item in his hoard, and the theft of so much as a single copper piece cannot go unavenged.  A Red Dragon will mercilessly hunt down anyone who dares to steal from it; if it cannot find the thief, it will begin to indiscriminately murder all nearby until someone gives up the thief.  Red Dragons have massive lairs that feature both high perches that allow them to see for miles as well as deep caves where they secure their hoards.  On occasion, these caves extend into the Underdark, and Red Dragons have on occasion come into conflict with the Mind Flayers.  If the Illithid manage to subdue the Dragon, they can force it to undergo ceremorphosis to become an abominable Brainstealer Dragon.   

Red Dragons are evil creatures who revel in destruction.  They never cooperate with each other unless they are facing truly world-ending threats, instead engaging in never-ending competition to see who can amass the most gold and cause the most destruction.  They are irrationally suspicious of all they encounter and create plans for every conceivable scenario.  Their paranoia rivals that of a Beholder.  There are few creatures in Faerûn that can stand toe-to-toe with a Red Dragon, but if a Red Dragon encounters an enemy that is notably more powerful that it, such a substantially older Red, Gold, Copper, or Silver Dragon, a Tarrasque, or extremely powerful Celestials, Fiends, or Archfey, it will not fight a battle it knows it cannot win.  However, once it initiates combat, it will not flee, even when given the opportunity to do so.  The shame of fleeing would destroy their social standing, and a Red Dragon would rather die than lose face in Red Dragon society.

The alignment of Warlocks that make a Pact with the Red Great Wyrm have little variation.  They are almost always Evil and are usually Chaotic.  Red Dragons are not senseless engines of destruction as they are often portrayed, but they can become psychotic butchers when they feel slighted or another Red Dragon one-ups them somehow.  It is rare, but some Red Dragons manage to throw off the fell influence of Tiamat and stop engaging in senseless violence.  Imvaernarho, also known as "Inferno," is one such Red Dragon.  He is a truly ancient Dragon, many thousands of years old, and he has focused on enriching his hoard above all other pursuits.  His hoard is estimated to be valued at "many dozen millions" of gold pieces.  Some Red Dragons have given up their murderous impulses to focus more on enriching their hoards.

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 avaricious creatures focuses on dealing massive amounts of fire damage, detecting hidden dangers, protecting certain locations with powerful glyphs, hiding treasures away where no one can get to them, and summoning powerful Azers, Fire Elementals, or Salamanders from the Elemental Plane of Fire.

Expanded Spell List

The Ancient Red Dragon lets you choose from an expanded list of spells when you learn a warlock spell.  You also gain the Fire Bolt 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.  Additionally, you learn to speak, read, and write Draconic.

Ancient Red Dragon Expanded Spells

One with the Flames

Red Dragons live in fire.  They lair in active volcanoes, their nostrils constantly emit tendrils of fiery smoke, the air around them simmers like a mirage, and their breath weapon is a cone of blazing fire.  They live in fire and have no fear of it.

Beginning at 6th level, you have absorbed this resistance as well.  You gain complete immunity to all forms of fire damage.

A Plan for Every Eventuality

Dragons love lairs with high perches where they can sit and survey vast amounts of territory with their sharp eyes.  They attack without provocation anything they believe they can destroy, swooping in and unleashing their fiery breath weapon before an enemy even knows they are there.  But they are also careful, paranoid schemers, creating a plan for every eventuality. 

Beginning at 10th level, you have advantage on initiative rolls as long as you are not surprised.  Additionally, you learn the Contingency spell.  You can cast this spell once and regain the ability to do so upon finishing a long rest, though you can use only one contingency spell at a time.

Overchanneled Fire

Fire Dragons have very precise control over their breath weapons, and they love to use them as often as possible.  They will send out small subtle bolts of flame to try to kill adventurers without destroying too much of their loot, but when they feel endangered, they can loose a seemingly unending gust of fiery destruction that consumes everything before it.

Beginning at 14th level, you can now enhance the damage caused by your fire-damage spells.  Whenever you cast a spell that deals fire damage of 1st through 5th level, you can cause that spell to automatically deal the maximum amount of damage.  The first two times you do this, there are no ill effects.  On the third time you use this ability before taking a long rest, you take 2d12 necrotic damage per level of the spell.  This damage cannot kill you, but if it reduces you to 0 hit points, you fall unconscious, lose all remaining spell slots and uses of your mystic arcanum, but are stable.  You cannot be awoken unless targeted by Greater Restoration, Heal, or a similar spell.  You will recover naturally over the course of 8 hours, during which you will benefit from a long rest. On using it a fourth time before taking a long rest, you automatically fall to 0 hit points, and you cannot recover except as described previously.