>>537783090
It was Orpheus's power, but Orpheus was unconscious the entire time. Emperor was using Orpheus's power to protect you. He commandeered it while Orpheus was unconscious, using his own mind manipulation psychic abilities.

The reason you don't immediately kill the Emperor is because there is no guarantee that Orpheus will protect you. If you use insight to get a feeling for what Orpheus is thinking while he's still trapped, all you feel is seething malice and the narrator tells you he would probably attack you on sight. Remember, he thinks you're an illithid thrall. So you need either the Emperor or Orpheus protecting you at all times, since even a momentary lapse in protection could make you turn if the brain ordered it at that time. That is why you can't kill Emps when you go in the prism the first time in act 1. But after you have the Hammer to free Orpheus, when you go in the prism in act 3, that's exactly what you do. You free Orpheus and ask him to protect you, and because he luckily is a wise and patient man, he decides to protect the people he knows are infected, for the larger goal of taking down the brain. It was all a big risk. If you kill or chase off Emperor and Orpheus simply says No to protecting you, then you turn into a squid. Which is what happens if you test the game and kill Emperor the first time you enter the prism, you turn into a squid and get a game over lol.