Board Thread:Questions and Answers/@comment-1031724-20160618003023/@comment-16058197-20160618095919

The nature of the process Qyburn subjected The Mountain to is deliberately kept vague to make it mysterious and creepy like Qyburn himself. In one episode, Jaime asks what Qyburn has done to Ser Gregor and Qyburn only replied with "a great number of things" without going into specifics. I think all we get to know as a viewer is that Ser Gregor is mortally wounded in the dual with Oberyn, but Qyburn saved him through some unorthodox method leaving him in some kind of zombified state. That The Mountain as we knew before is dead is quite clear, as I think the former Mountain would just kill the Lannister soldiers barring Cersei from attending her daughter's funeral and would also brutally slaughtered the Faith militants that tried to arrest Cersei. The "new" Mountain is stronger than he was but is little more than a tool of Cersei and Qyburn. I doubt Ser Gregor before he was treated by Qyburn would do nothing more than escorting Cersei to her room and killing those standing in her way.