Revealing mistake: Watch Elena's monitor screen just before she taps some keys and gets the display of information about the XV773 freighter. It's filled with a mass of tiny text which initially looks like just gibberish - but if you look closer, you'll see it's actually the computer program used to create the information display. Someone has even typed in the RUN command at the bottom of the screen, so that all the actress had to do was press the ENTER key and an instant faked "information readout" appears.
Attack of the Cybermen - S22-E1
Revealing mistake: When Lytton stabs the Cybercontroller, some of the Cybercontroller's 'blood' gets splashed on the camera. (The 'blood' is green-dyed water spraying from the Cybercontroller's arm.).
Revealing mistake: After the TARDIS breaks down the Doctor and Peri can be seen reading the manual, although it is clearly a book of empty pages.
The Trial of a Time Lord 9-12 (aka Terror of the Vervoids) - S23-E3
Revealing mistake: In episode 12, while the Vervoids are dying, look out for the ones wearing sneakers and tracksuit pants (complete with drawstrings)...
The Trial of a Time Lord 13-14 (aka The Ultimate Foe) - S23-E4
Revealing mistake: In the final episode, Glitz and the Master leave the console room while the Doctor is driven into submission, but they are quite obviously standing by the scanner screen.
Delta and the Bannermen - S24-E3
Revealing mistake: The bodies lying on the ground during the initial battle are rather too obviously rubber dummies rather than real people.
Dragonfire - S24-E4
Revealing mistake: At several points in the story the 'huge heavy ice cliffs' get blown fractionally upward by people running past them, showing that they are made of very thin, very light plastic.
Remembrance of the Daleks - S25-E1
Revealing mistake: When the Doctor slides with his umbrella from Coal Hill School to the Dalek spaceship, he is obviously not played by Sylvester McCoy. He is much too tall.
Revealing mistake: When Ace and Susan are sitting underneath the huge pipe about to be executed by the Fondant surprise, it's obvious that the actresses aren't sitting directly underneath the pipe, but slightly behind it.
Revealing mistake: In episode one, as the Doctor is repairing the buggy, one of the patrol runs on too soon, realises that he's come in ahead of his 'cue', and runs back.
Revealing mistake: When the Doctor taps the ice crystals, they wobble instead of breaking.
Revealing mistake: When Ace is being attacked by the Haemovores, she strikes one of them on the head, causing its mask to go up and revealing part of the actor's neck.
Revealing mistake: When Fenric (having possessed the body of Judson) knocks over the chess pieces on the board, watch one piece (The King) in particular. You can see a 'hinge' made of white sticky tape attached to the board and the base of the chess piece, presumably there to stop the chess piece rolling away onto the floor.
Revealing mistake: The shot of the two motorbikes colliding with each other and exploding into flames is very unconvincing. Watch carefully, and you can "see the join" where a shot of the two motorbikes passing each other (and NOT colliding) is replaced by a "staged" fiery explosion.
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.
Daria Sigma