The MSX2 adaptation of Castlevania, this game pre-dates almost the entire series. Released in Japan, Europe, and Brazil, but not the U.S., it's pretty much a lost footnote at this point. For whatever reason, it hasn't been ported to any modern collections. They forgot about Vampire Killer, much like people once forgot about Dre.
Gameplay-wise this is much closer to the NES game than the arcade Haunted Castle was, and follows the Metroidvania formula that later games in the series would frequently adopt. Well, sort of. It still takes place within confined stages, they're just more of a maze than a simple point A to point B. Which makes this...the first Sorta-Metroidvania in this series. The Protovania.
Note: Castlevania Bloodlines on the Genesis was also called Vampire Killer in Japan, but it wasn't a remake of this game or anything.
