Revealing mistake: At the climax, when the Doctor and Sarah are setting up the scarf trap, the Doctor bumps a rock, which wobbles.
Continuity mistake: In Episode 1, the TARDIS crew pass out from the change in pressure as they descend into the Earth. However, at the end of episode four, they climb out on foot and suffer no ill effects.
Revealing mistake: When Jamie is wrestling with one of The Ice Warriors in a storage room, one of them gives the wall an almighty knock and it nearly falls down.
Plot hole: In episode 1, on both occasions that Silas P presents his card (first to Daphne S, then later to the Doctor), he gives it to his victims the wrong way around. They have to surreptitiously turn it over so that the side with his name on it is facing them, and then act surprised when he tells them to flip the card over to reveal the words "Happiness Patrol Undercover", as if they hadn't seen it before.
Other mistake: What happens to Tegan's bag when the plague victim transforms into the cavalier? It doesn't appear to be left behind, even when the cavalier later vanishes.
Other mistake: In episode 3, watch the scene where the co-pilot is shooting; you can see his pants rip straight down the seam at the back - which unfortunately happens to be the part of him facing the camera at the time. He then wanders around for most of the rest of the episode with the tear in his pants plainly visible.
Plot hole: Peri makes no mention of the Doctor's heroic sacrifice on her behalf, nor thanks him for it (no wonder he's touchy).
Continuity mistake: In episode 2 of "Survival", Midge is captured, and the sabre tooth he's carrying gets knocked to the ground. Neither he nor the Master pick it up before they teleport to Earth. Yet in Episode 3, the Master is able to present the sabre tooth to Midge as he's about to ride his motorbike towards the Doctor.
Plot hole: The Doctor and Romana comment on a recording which has finished playing before they have entered the room. Not only that, but all the other characters behave as if the Doctor and Romana had seen this recording.
Continuity mistake: After the Doctor helps Romana over the cliff, the stock footage of a sun setting over a calm sea does not come close to matching the total darkness and stormy seas in previous shots.
Visible crew/equipment: When the Doctor and Kimus are breaking into Xanxia's room, an ordinary telephone is visible on the right of the screen.
Invasion of the Dinosaurs - S11-E2
Revealing mistake: In episode four, when the Doctor is being herded through the complex, the walls wobble very badly whenever the metal shutters slam down.
Plot hole: When Della gets shot in the face in episode four, she clutches her stomach. (What is even more remarkable about this error is that this keeps happening over and over again: someone gets shot and falls to the ground, clutching their stomachs, regardless of where they have actually been shot. See the error in Season 14's 'The Deadly Assassin' for an example of the SAME error occurring).
Continuity mistake: In the scenes set in the underground tunnels in Part Three, the Kandy Man has no metal brace around his mouth, but he does have the brace in other scenes.
Underworld - S15-E5
Revealing mistake: The CSO caves are awful throughout, but one of the worst incidents is in episode three when Leela talks to Idas about a revolution and they both run right through a rock.
Revenge of the Cybermen - S12-E5
Continuity mistake: The use of gold against the Cybermen is wildly inconsistent in this episode. It is said that it suffocates them. Yet Cyberman have been seen functioning perfectly in vacuum ("The Moonbase" and "The Wheel in Space"), it affects the Cybermats, who are little more than metal drones, and it affects the Cybermen's radar, which does not breathe.
Revealing mistake: In the finale, when Stevens is beating on the computer console, it moves around quite a bit, even thought it is supposed to be a strong and stationary object.
Revealing mistake: Geoffrey Hinsliff (playing Fisk) accidentally refers to Tryst as "Fisk" at one point.
The Evil of the Daleks - S4-E9
Visible crew/equipment: When the Doctor and Jamie enter the secret room watch the top left corner. A boom mike shadow appears and then moves out of shot.
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.
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