In this small room, you'll find a Succubus and a Lilith. It will slowly gain momentum until it smashes right through the right wall, gaining you access to the next room. This leads you back to a vertical corridor we've been to already. Then, a hand comes from the background and crushes the bat, and the boss fight begins. Once you reach the end you will find a dead end with a huge wrecking ball. You'll be, quite literally, in an elevator shaft. Equip it if you so desire. Jump across to the save room again, save and heal, then go back left to the previous corridor once more.