Complex sentence: The offspring between humans and vampires resulted in four levels of vampires, characterised by the amount of human blood, a Level A having no human blood and a Level E being a former human; with levels B & C falling somewhere in between.
Split into simpler sentences: The offspring between humans and vampires resulted in four levels of vampires, characterized by the amount of human blood. A Level A vampire has no human blood and a Level E being a former human; with levels B and C falling somewhere in between.