Vampire Killer (MSX2)
Vampire Killer was Konami's first game for the MSX2 home computer (the successor to the original MSX). It's an alternate take on the original Castlevania and follows the same basic premise as its NES counterpart, but with a different weapon/item system and an added emphasis on seeking out treasure chests and acquiring keys to clear each stage.
By loading Vampire Killer with a Game Master cartridge inserted in the second slot, you can access a cheat menu just before starting the game that allows you to skip to any stage and adjust the starting number of lives.
Extract the hidden backgrounds shown in the source linked, and upload them here.
Some areas in the game have extra background graphics that are hidden by the status bar at the top. Thus, these are never seen in-game.
Examples include the first level with the area outside the castle and one of the staircases, and the final boss area.
Like most Konami games released on the MSX, Vampire Killer has a region detection code that will change the game's language and settings depending on the hardware it's running on. In this case, it will change only the title screen, displaying the Akumajou Dracula title when running on a Japanese computer, and Vampire Killer when it's on a European computer.
Since the MSX2 Dracula contains its export counterpart Vampire Killer in its programming, this has led to the popular belief that Vampire Killer predated Castlevania... which is partially true in a sense. The Famicom Disk System version of Dracula was released a month before its MSX2 counterpart in Japan and both games appear to have been developed in tandem due to their close release dates, but the Disk System version had no such region switch. Vampire Killer wasn't officially released in Europe until 1987 (as evident by the copyright date on the box and manual), the same year Castlevania was released on the NES in North America.
It is worth noting that Konami later released a third version of Akumajou Dracula for the arcades titled Haunted Castle outside Japan, showing that Konami experimented with different overseas titles for the series before settling with Castlevania. The title Vampire Killer would later be used for the Japanese version of Castlevania Bloodlines.