Darth Bane VS Darth Zannah on Ambria. Life essence Transfer was the result. Bane transferred his life essence into his apprentice Zannah. But kept It a secret from everyone. And went on portraying Darth zannah. BRILLIANT. He combined his immense Knowledge and secret organizations with his apprentices Power of dark side sorcery. And double bladed LightSaber Techniques. My favorite sith Lord.