Do you wonder where the Sengir Dagger derives its name from?
Back in '94 when Wizards of the Coast and Richard Garfield were designing the original Jyhad right (after they had published Magic the Gathering (MtG) a year earlier), the word Sengir got somehow transferred from MtG to VtES.
In the first MtG edition ("Alpha") the card "Sengir Vampire" is a black creature card with 4/4 and flying which gets a +1/+1 counter each time the Sengir Vampire is damaging another creature and moving it into the graveyard. The card has been reprinted multiple times, with M2012 being the last expansion where Sengir Vampire was included.
So what's all this fuss about Sengir vampires, what are they exactly. Well, they don't actually fit in the whole World of Darkness of White Wolf. The background story is completly separate.
Sengir is the name of vampire race in the MtG multiverse (allegedly similar to the similar to the Nosferatu breed). Sengir Vampires are said to be descendants of the legendary Baron Sengir on the planes of Dominaria and Ulgrotha.
Apparently the infamous Baron Sengir is the founder of this particular breed of vampires, as described in the book Secrets of Magic. He's ruling his the Dark Barony on Ulgrotha from Castle Sengir. A whole more information on Baron Sengir can be found in the MtG Salavation Wiki.
Currently there have been nine cards published with the name "Sengir" in its title, namely: