Castrovalva - S19-E1
Question: Why does The Master come up with these ridiculously elaborate plans to kill The Doctor when he could have killed him at the beginning of the first episode, just after his regeneration, when he was very weak?
Earthshock - S19-E6
Question: In Earthshock, season 19, at the end of episode 3, the Cyber Leader views his troops marching down the corridor. Each column is headed by a Cyber Leader. Is this a mistake, or is there more than one Cyber Leader allowed per army?
Answer: In 'The Five Doctors', three separate Cyberleaders are definitely used. So it's likely that Cyberleaders are like unit commanders, of which a fair-sized army might have several.
Chosen answer: Because he wouldn't be satisfied simply killing The Doctor when he's weak and infirm. The Master needs to outsmart him.
Captain Defenestrator