Board Thread:What If?/@comment-5674726-20140630220202/@comment-6047958-20151002005256

It's also possible that Nimueh was playing mind games with Merlin and trying to make his friends turn against him by convincing him that he had to take a life to save a life. "It is not magic that has done this, it is you," Merlin told her, which hints that that was just Nimueh's way of doing things and it would be different for him. He just used her life to restore Gaius' because she was the one who had taken Gaius' life.