Stop its attack on the servant in the upstairs bedroom (the one on the right). Attack it until it retreats and you see an intermission sequence of it "refueling". Talk to the servant and he will give you the Gun Cabinet Key. Take it to the other bedroom and unlock the gun cabinet, liberating the Elephant Gun. Track down the vampire creature two more times and it will drop the top half of the Basement Key. Mix the two halves and enchant the broken key to fix it. Then, enchant the Elephant Gun with the Strong Alignment and go to the basement. The first thing you should do is shoot the relic in the corner with the Elephant Gun (double barreled). Go back upstairs to reload so it cannot get you. Once the relic breaks you can attack the creature.