Continuity mistake: When Karra dies and turns back into her human/humanoid form she is wearing a black top that they did not wear as a Cheetah Person.
Battlefield - S26-E1
Character mistake: The Brigadier asks the pilot if she speaks Czechoslovakian, even though Czech and Slovak are different languages.
Revealing mistake: When the Doctor and Leela are confined to the officer's quarters, look at Leela's eyes after she sits down; one of her brown contact lenses has fallen out, revealing her real blue eye.
Remembrance of the Daleks - S25-E1
Continuity mistake: When the Doctor and Ace steal the military van they leave the doors open, but in the next shot when we see the van leaving Totters Lane the doors are suddenly closed.
Continuity mistake: The Doctor's hair goes from being messy and extremely curly in the TARDIS scenes to being combed and much less curly in the scenes set outside the TARDIS.
Continuity mistake: When the Doctor picks up the humanoid skull his hat is looking normal but in the next shot the brim of his hat is folded down and completely flat. In the next shot it's back to not folded again.
Continuity mistake: In episode 4, Skinsale is murdered by the Rutan on the stairs right outside the crew room but later in the episode when the Doctor and Leela runs down the same stairs, Skinsale's body is not there.
The Masque of Mandragora - S14-E1
Continuity mistake: When the Doctor is explaining about the Mandragora Helix, his scarf goes from being over his shoulder, to behind his shoulder and back.
Continuity mistake: When the Doctor enters the desert room in addition to his coat, he is wearing a brown waistcoat with a white shirt underneath. When the shot cuts away and the back to the Doctor, we see him take off his coat but he is no longer wearing the waistcoat. Later when he collects his coat after the acid bath scene and he starts to look through the wardrobe for a disguise he is mysteriously wearing the waistcoat again.
Remembrance of the Daleks - S25-E1
Other mistake: Right before the Doctor gets attacked by the destroyed Dalek he says: "Let me see, Professor" but the subtitles says: "That's impressive."
Audio problem: In Part 3 when the Brigadier gets behind the sand pile with Arthur Ollis, the Brigadier asks him "Did you find a way in?" This is not Nicholas Courtney's voice for this one line. He speaks again right after that and it is his voice. (00:13:20)
Revealing mistake: In the last part, the giant robot steps on a soldier. There are several things wrong with this scene. 1) You can see the matte halo around the robot's foot. 2) The robot does not leave a footprint. And 3), after the soldier gets squashed, his arm is visible waving over the robot's foot.
Revealing mistake: Matte halos appear very frequently in this episode, particularly when descending into the mine shaft.
Revealing mistake: When Jo and the Doctor are rowing through the maggot lake, several times parts of the actor's arms disappear.
The Moonbase - S4-E6
Audio problem: In part 4, when the Cybermen are outside The Moonbase controlling the workers, the mouth of the radio operator does not move when he is speaking to them. Furthermore, a few of the Cybermen's mouths outside The Moonbase are stuck open when they have no dialogue.
Visible crew/equipment: When the group are thrown into a dungeon in Omega's palace, you can see tape in the corners which is holding the set together.
Planet of the Spiders - S11-E5
Revealing mistake: When Mike and Sarah are in Mike's car going to the monastery, the car swerves off the road and Mike is replaced by a stunt man.
Factual error: In Episode 3, Zarof fires a gun. The muzzle is seen and a sound is heard but the gun doesn't move and there's no smoke or bullet, no flash or anything at all. (00:23:05)
Revealing mistake: In episode 1 when the Doctor is checking the controls you can see the studio lights to the top left corner where the set doesn't completely connect.
Continuity mistake: Towards the end of episode 2 it's nighttime, but when Ian and the Doctor lure the Dalek over from the TARDIS, and when it falls, it's daylight.
Chosen answer: The Master is insane. If he can't control the universe, he'd rather see it destroyed.
Captain Defenestrator