Other mistake: William has a bit of a nightmare, completely throwing the others during one scene by saying the same line ("It's not very likely") twice, and fumbling the line "You knocked both Susan and I unconscious". He also omits the scripted explanation for the melted clocks.
Other mistake: The Tyrannosaurus rex which appears in this story does not actually roar; instead it says the word 'roar' several times. There may be little scientific evidence as what sound a T. Rex makes, but it is unlikely that any of them spoke fluent English.
Other mistake: Ian has completely forgotten the distinctive shape of a Dalek. It's only when the Dalek starts speaking that Ian says to the Doctor, "that voice". Yet later when they are at the saucer, he talks to the Doctor about the new back of the Dalek having a disk on them now.
Add timeMatty W
Other mistake: The Cyber Leader is supposed to follow the Master's footsteps exactly in order to get across the chessboard. He doesn't. This cannot be classed as a character mistake because the Cyber Leader knew what was involved. I believe this mistake was caused by the actor not being able to see the chessboard through his helmet.
Other mistake: In episode 4, as the Doctor, Tegan and Nyssa are being led away from the bridge, the Cyberleader loses his footing when he gets to the bottom step, and stumbles/trips up (He recovers himself very quickly; so quickly in fact, that this mistake was left in the finished episode).