Complex sentence: First mentioned in the series' pilot and then in the episodes "Descent" and "Bloodlines", the House of Leichen consists of vampires that have sworn off of killing humans, and drink only cloned blood.
Split into simpler sentences: First mentioned in the series' pilot, and then in the episodes "Descent" and "Bloodlines". The Leichens are vampires that have sworn off of killing humans, and drink only cloned blood.