The Clot Vampire
The clot vampire and its spawn are truly horrific creatures,
both undead and aberrant, that are the result of an alien
parasitic infection from outside reality. The true clot vampire
itself is made almost entirely of shifting, sapient blood, but
may take any form it wishes to deceive its prey, though it must
tasted a beings blood to masquerade as a specific entity.
They are very hard to kill, and can exist without any sustenance
at all for centuries, only to rouse themselves again at the first
opportunity to drink the blood of the living. They are also
extraordinarily contagious, infecting any who they bite, or who get
any of the clot vampire's blood in their mouth in a fight.
An infected creature becomes a clotspawn, and only after drinking
a great deal of blood and the passage of time can they become a
full clot vampire. Normal weapons cannot harm them, and even
a magical weapon must be silvered to have its full effect.
The sun does not burn this sort of vampire, but they do tend to
operate at night, when they can regenerate.
In combat, they extrude tentacles of blood, to strike, to grab, to
draw prey near.