If you happen to come across a vampire, your only recourse is to run and hope it gets bored of you. They are killers, through and through. They feel no remorse, no grief, no pain. They will tear you limb from limb, and at best, grow irritated that your blood stained their clothes. — Dissection of the Supernatural
Vampires are a type of exceptional powerful Undead that feed on the life force of other creatures. Their power stems from their curse, which in itself is drawn from the Shadowfell, and no living creature is safe from the curse - humanoids, giants, even dragons can succumb to the curse and be transformed into baleful creatures of the night.
Description
For the most part, a vampire retains the appearance they had in life, with few albeit major differences. For one, the creature's skin turns pale, and their features sharpen into a feral visage, giving them a predatory aspect. Regardless of their eye colour in life - provided they have eyes - their eyes become crimson red, granting them the ability to see perfectly in any darkness, both magical and mundane. From their hands they sprout claws, and from their mouth protude impossibly sharp fangs. These claws and fangs appear to be made of the same glass-like substance and are both retractable. Vampires also do not cast a shadow and cannot be seen in mirrors.
However, a vampire is still undead. Undeath preserves most creatures, slowing rot with the stagnant magic of the shadowfell, and the same is true for vampires. A well-fed vampire appears the same as in life, albeit changed as described. But should they fail to feed, the curse grows stronger. Their feral features grow sharper, and the stasis of flesh begins to weaken. The longer a vampire goes without feeding, the more rotten and decayed their flesh appears; a cruel irony for those seeking the immortality of undeath. To this end, many aged and decayed vampires will wear masks to hide their appearance from mortals, but also from their vampire peers. A hungry vampire is a weak vampire.
Abilities
A vampire retains all the abilities they had in life, but upon full maturation of their curse they gain several new abilities. Foremost is their ability to drain the life force of a creature through their claws or, more commonly, their fangs. Most vampires accomplish this by biting the creature and drinking their blood, draining the energy from the creature's crimson ichor. This life energy sustains them and their curse, but also grants the vampire the ability to regenerate their wounds.
Additionally, a vampire is blessed with a large amount of shadow magic, which they mainly used to transform themselves. They possessed the ability to transform themself into a misty, gaseous form. In this form, they appear to be made of the stagnant, unshifting fog-like mass that makes up the shadowfell. They could also use this power to take the form of beasts, such as rats, bats or wolves. A particularly adept vampire could use this ability to transform themself into much more complex forms.
The curse also amplified much of a vampires physical abilities, increasing their strength, dexterity and durability tenfold. A creatures senses also become enhanced, as vampires can see through any darkness, have impeccable hearing, and their sense of smell is far greater than that of mortals. As the curse grows in strength from a vampire unable to feed, these traits grow stronger, whilst their magical abilities grow weaker. A completely feral vampire - one that has not fed in weeks - is as strong as a giant and as fast as a quickling.
Weaknesses
As with most creatures associated with the shadowfell, vampires are especially weak to sunlight and light-based magic. If exposed directly to the light of the sun, they begin to take damage, eventually burning to ash if they do not hide in the shadows. Despite common belief, vampires are not averse to running water or garlic. Like most undead, their interactions with potions and poisons become inverted; health potions cause harming, harming potions cause healing, poisons are medicine and medicine become like poison.
The shadowfell is a place of order, and as a result, vampires have a unique weakness to chaotic magic, which can be drawn from the Feywild. As such, many vampires choose to settle far from confluxes and other areas of latent wild magic.
Curse of Vampirism
Vampirism is a curse wrought of shadow magic, which vampires are capable of spreading further like a disease. When biting a creature, a vampire can occasionally pass the curse of vampirism into that creature's blood. Over the next few days, provided it survived the feeding, the creature becomes lethargic, weak, and develops a distaste for the sunlight. On the third night, if the creature succumbs to the curse, it dies and is reborn as a vampire spawn. For these spawn, the curse is only in its fledgeling state; they become stronger, fast and more durable, become able to regenerate, but also begin to develop the vampire's weakness to sunlight as well. They also gain none of the vampire's magical abilities, only the physical ones, and cannot drain life to sustain themselves. Once transformed into a vampire spawn, the creature is compelled to seek out the vampire that created it and until the curse manifests fully, the spawn is bound to the vampire's will.
The curse develops over several more weeks, and if the spawn is not slain by the vampire that created it, it develops into a fully-fledged vampire. From then on, they must feed frequently to sustain themselves, lest the curse consume them completely and their unlife is brought to its end.
There are other ways to manifest the curse of vampirism. Shadow magic rituals, blood rituals with the blood of a vampire, transmutation rituals fueled by shadow magic and more. Undeath is a boon sought after by many. On occasion, when these rituals fail, it can instead transform the creature into a Dhampir, a mortal race influenced by vampirism but not fully consumed by it, torn between the worls of life and undeath.
Society
Vampire society is scarce, with the creatures rarely forming into organised cultures. Small sects of vampires might band together in times where easy food is scarce, but most vampires are too possessed of jealousy and suspicion to surround themselves with peers. Many vampires also surround themselves with lesser undead - ghouls, ghasts and the like - to defend themselves.
However, any exception can be made for the minute and isolationist nation of Duskhold in northern Irral. Nestled in a small valley in the Spine of the World, Duskhold is a nation ruled by vampires. In exchange for blood from the peasantry, they bestow upon their subjects the knowledge and possessions they have obtained over millenia. Here, vampires are free to walk in the day, as a black cloud of magic blots out the sky.
This is no paradise, however. Vampires are forced to ration themselves on the limited blood supply available, leading to many becoming irritable on the brink of starvation. Betrayal and jealously schemes behind every dark corner, only kept in check by the Dusk King Dragos and his iron hand.
Lairs
Should a vampire grow in power enough to want a lair of their own, they often choose grand yet defensible locations near to sustainable food sources, such as old castles, manors or abandoned abbeys on the edge of country towns. Here is where they amass their wealth and defend themselves from would-be warriors of the light. It also serves as a secure retreat for when feeding goes terribly wrong.
Life in Death
Most vampires retain their memories and personalities from life, but they become twisted by the curse. Once benevolent creatures might become vindictive and petty, while love can be twisted into obsession and jealousy. Most of a vampire's emotions - save for hunger, rage, jealousy and other such negative feelings - are dulled while the curse is at its strongest, only returning when it fails to feed.
Because of this, most vampires seek material fulfillment, surrounding themselves with objects that once brought them joy. Akin to dragons, they use their immortal lives to amass a great wealth of material posessions, in hopes it will bring them some small modicum of joy. In fact, some vampires are known to go without feeding for several days just to regain some of their emotions.