Night of Wallachia

His name originates from Wallachia, in Romania, which is where TATARI first came into being. His backstory is that rumors of Vlad the Impaler, whose life story became the basis for Dracula, became TATARI. Zepia challenged The Sixth (Program No. 6/ The Sixth Law), which led to his defeat, and in turn allowed him to successfully imprint himself as a phenomena of the world. Night of Wallachia has completely calculated all possible outcomes of the world, and now he is an enigmatic Dead Apostle who “occurs” at pre-calculated areas in the real world through the materialization of rumors. For more details, see Sion’s dialogue in the Melty Blood K Route “Summer Illusion, King of Fallacy.” Also “Program No. 6” mentioned at the start of the story mode refers to The Sixth which Night of Wallachia challenged.

MB Official Strategy Guide: Melty Blood Glossary

A member of the 27 Dead Apostle Ancestors. One who tried to embody eternity not as a living being, but as a phenomenon. Tatari.
A Dead Apostle with the unique ability to converge upon rumors in a region and materialize them for a single night. Because it takes the form of what the people fear the most, they can neither defeat it nor escape it. The “Night of Wallachia” specifically refers to the reality marble that shuts away a town in that horror movie-like world.
When he was still a normal Dead Apostle, his name was Zepia Eltnam Oberon. Even after inheriting the position of number thirteen among the Dead Apostle Ancestors, he yearned for still more power, and became the phenomenon “Tatari.”
Of course, that was nothing more than a means to an end—his true objective lay elsewhere. Unfortunately, though, he was unable to accomplish it, and he drifted through the world as the Tatari to the bitter end.

MB Act Cadenza PS2 Manual: Tsukihime Dictionary

Cryptic vampire who manifests the phenomenon TATARI – a materialization of fear and uncertainty present in society.

MB Back Alley Alliance Nightmare: Encyclopedia of Rojiura Nightmare