Vitreous

Vitreous soaks in slime that covers half the room. Stepping into the slime hurts you, so somehow you have to get it out of there. First wipe out Vitreous's children (?) as they fly at you. They don't seem very bright, so facing up and swinging the sword over and over is enough to beat them. Pick a spot where the lightning Vitreous fires now and then can't reach you, though. When Vitreous charges, angry at losing its children, stand at the bottom of the room with the sword held out. Swinging the sword around is more dangerous.