Please don't read if you are not up to encontro, data in Game of Thrones or if you plan on reading/watching it.
But I came across this theory regarding Arya and the Waif. When the Waif was hunting Arya, Arya cut the candle and the room was dark, and we assume that Arya kills the Waif in the dark. But since it happened in the dark, and the body of who died was unidentifiable, what if..... the Waif killed Arya and the Waif has taken Arya's face? I just think of it as a major mindfuck to think that all this time Arya has actually been the Waif using her face, as that was the Waif's intentions all along. There are holes in this theory but I still actually really like it.
