The Legend of Qin Season 1 Episode 5 E 5

As the group recovers from White Phoenix?s recent attack, they discover something shocking: it was Yuer who betrayed their location to the League of Assassins! Yuer's secret is that she is a former princess of Yan, one of the kingdoms that had been conquered by Qin. Her family is now homeless, and she believes that her father was killed by Gai Nie. As a result, she hid her hatred for Gai Nie, and fed him poison while he was recovering from his wounds, a poison that makes him unable to use his legendary sword. With Gai Nie weakened and unable to fight, the League of Assassins expert snake charmer, Crimson Snake attacks with her serpents. Master Ban uses a mechanical creation to defend the group against the snakes. However, the device goes out of control and attacks Yuer, knocking her off a cliff.