There are beings of immense power and horrific weakness who have found ways to extend their life beyond the norm – and are not undead, but Undying – immortal, though the manner of that life leads much to be desired.
The two best known examples of this are Liches and Vampires.
Vampires are a scourge that first appeared following a bloody civil war, with a member of a minor Noble house making a deal with one of the infernal courts and gaining significant power as a result — but at the cost of his humanity and his soul.
Vampires derive their great power from a peculiar, forced fusing of the three great Lower Planes, fusing a potent mix of Necrotic, Nether, and Infernal energies together through the original bargain that created their kind with Asmodeus, the Black Heart of Hell itself.
Vampires have no Soul and survive without by feeding their Spirit and Flesh at the price of their Heart. It is the consummate joke to realize that Vampires exist because of intense emotion that drove them, only to become something that lacks in all but the vilest of permitted Infernal emotions due to the machinations of the most powerful of all Devils.
They are neither dead nor alive, having become something else. The original and Prime vampire is long dead, but he had three “children”, or people whom he turned into vampires and bound within the same curse that he had been bound by.
Vampires are entirely territorial, limited to the realms in which they were born and a connection to the very soil itself. Vampires cannot stand the purity of the Sun, and have challenges with fire, which can harm them in any of their forms. Vampires are not stronger than they were in life, but they are generally faster and less limited by sensations such a pain — for they do not feel such things, and are incapable of love, contentment, and friendship.
A group of vampires is headed by a Master. The master vampire is always going to be the oldest, and they will always have three people beneath them, and those in turn, will have three, and those then will have three, and so forth. A vampire does not always turn others — doing so is weakening, and not all seek to reduce their own power. They can compel others, to induce a loss of memory, and they are utterly and completely without any redeeming qualities. They can change form into a thick black smoke or take the form of a rat or a wolf. The stories about bats are a myth — vampires do not fly, though they do have very strong and very sharp claws, allowing them to scale surfaces and their lack of fatigue means they do not tire.
Vampires need to sleep upon the soil of their realm of birth, and they need to be hidden from the sun. Some have cabinets in which they rest during the day, lined with the soil, so that they can travel.
Vampires can be killed much the same as anything else can, though the best ways are still fire and any other great source of Purity (including running water, which can drown them and tear them apart, though this can take significant time). A vampire is ranked according to how deep their lines of subordinates go, so a vampire with none is a rank one vampire, while one that has five generations is a rank five (each generation consisting of three answering to one above).
Vampires can command undead. Vampires are always empowered by evil, but weakened and subject to the powers of the Powers That Be who oppose those forces. Some call Vampires “anti-paladins”.