Genesis of the Daleks - S12-E4
Revealing mistake: During the Doctor's early conversation with the Time Lord, there is fog swirling around them. When the Doctor agrees to take on the mission, it suddenly appears very concentrated around the tip of the rocks behind them, as if generated from a source behind the rocks. Normal fog would not do this, and it's clear that dry ice was used as the fog effect (DVD commentary confirms this). (00:02:45)
Genesis of the Daleks - S12-E4
Revealing mistake: When Ronson is killed by The Daleks, you can see Ronson reacting a little too soon to the Dalek laser. (00:14:40)
Genesis of the Daleks - S12-E4
Revealing mistake: In episode 6, when the Thals detonate the charges, smoke is seen coming through the door before the detonator is pressed down. (00:19:40)
Genesis of the Daleks - S12-E4
Revealing mistake: Whenever there's a close-up of Davros, it's very easy to see that there's a gap around his mouth where the mask should blend in with the actor's face, but doesn't. This mistake was rectified, incidentally, in Davros' next appearance in "Destiny of the Daleks."
Revenge of the Cybermen - S12-E5
Revealing mistake: At the climax of episode four, the Beacon plunges close to Voga and orbits very fast before the Doctor manages to break free. The planetscape that appears on the screen is quite obviously a revolving drum with bits of clay on it.
Revealing mistake: In episode four, when Caber breaks a piece off the Zygon equipment, the entire wall shakes.
Revealing mistake: In episode four, when Vishinsky and Sarah go into the storage room to get the force field generators, the plaque on the door flops around like the cardboard that it is.
Revealing mistake: The "crystal" tube holding Sarah wobbles whenever it is touched.
Revealing mistake: In order to save money filming the lift-off of Crayford's rocket from Oseidon, the producers decided to use stock footage of a Saturn 5 blast-off. Unfortunately, that meant the words "UNITED STATES" in large red lettering are seen on the side of the rocket...which is a little bit of a giveaway, especially as the rocket is supposed to be a BRITISH space probe.
Revealing mistake: When the Morbius creature falls over the cliff, he bumps into the camera.
Revealing mistake: The fake snow in episodes one and two is effective - with the exception of when the Doctor is digging up the second Krynoid pod, where it is painfully obvious the snow is styrofoam packing peanuts.
Revealing mistake: At the climax, when the Doctor and Sarah are setting up the scarf trap, the Doctor bumps a rock, which wobbles.
Revealing mistake: Watch the scene where Uvanov sticks a Laserson probe into the head of one of the Vocs (V4) as it is strangling the Doctor. After he shoves the probe in, you can quite see the suit's helmet come away from the rest of the suit.
Revealing mistake: Watch really closely when Leela throws the knife at one of the robots. You can see the knife fall to the floor about a second after she throws it. Then, of course, the next shot shows the knife sticking out of the robot's chest. Guess Leela isn't quite as good a shot as we thought.
Revealing mistake: When the Doctor and Leela are put in Uvanov's cabin to await questioning there is a shot of a robot listening to them in which you can see the actor's neck.
Revealing mistake: When SV7 comes into Taren Capel's workshop, its usual eyes are missing - only black discs are visible (later in the scene, these are overlaid with the red speckled pattern to show the robot being reprogrammed).
Revealing mistake: When Taren Capel is modifying a Voc robot, there is a shot of the robot's agitated hands as he reassures it. On the robot's silver gloves, the "Marigold" logo is visible. ('Marigold' make rubber gloves that are used when washing dishes). Perhaps that particular Voc robot had been assigned to dish-washing duty that day...
Revealing mistake: When the Doctor confronts D84, the robot is shown in profile as the Doctor forces it to speak. The movement of the actor's jaw is visible behind the mask.
Revealing mistake: Immediately after the Doctor stabs SV7 in the back of the head and the robot crashes to the floor, the next scene shows the fallen figure of SV7 in the background - breathing heavily, with his chest moving up and down.
Revealing mistake: Near the end of episode one, the Doctor peers into a hopper and sees ore piling up inside. The image of the ore wobbles back and forth.
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