Complex sentence: To use the process, the original is first killed or destroyed; but, in at least one episode, a human who is supposedly killed later revives in hospital, even though his Mysteronised double is alive and walking the Earth Episode 21.
Split into simpler sentences: To use the process, the original is first killed or destroyed. However, in at least one episode, a human who is supposedly killed later revives in hospital, even though his "Mysteronised" double is alive and walking the Earth Episode 21.