Deliberate mistake: The shot of the mothership landing bay and the arrival of Charles' ship is stock footage that has been used several times before. There is also a continuity error here - the view from the landing bay shows darkness outside, but the next shot shows broad daylight. (00:06:20)
Revealing mistake: The two Elizabeths are both played by the same actress, except in the shots where both are seen together. Continuity mistakes in the second Elizabeth's death scene reveal this, such as the second Elizabeth's head position changing, and the first Elizabeth's jacket being open/closed between shots. (00:42:30)
Continuity mistake: When the spaceship is hovering overhead, we see various shots of the Maxwell family and others. In one shot we see the family from behind with a person in blue. We then jump to a shot from the front with that person not in picture. We then go to another behind shot and see the same person hurriedly moving into shot. (00:10:20)
Continuity mistake: Mike Donovan (riding a horse) is chased by a Visitor shuttle. It is obvious that there were recycled some shots from "The Final Battle" (Ep. 1). In "The Champion", Donovan does not have a laser pistol. However, there are some shots in which he has that pistol: obviously, those shots are taken from TFB.
Revealing mistake: When the two wildcats throw hand grenades at the Visitors, the grenades are obviously fake because the explosions do not occur at the same place as where the grenades land. The detonations have obviously been located in a safe place away from the actors. (00:11:50)
Deliberate mistake: The shot of Willy running away from the parked car is taken from the episode where Elias is killed. Two things give this away - 1) Willy is wearing a different coloured jacket and 2) he is supposed to be seriously injured yet he sprints along the street. (00:08:50)
Continuity mistake: When Charles reads the message about Nathan Bates coming out of the coma, there are two things to look for during the closeup of the note. The logo on the top is replaced by writing and he grips the note in a different position from before. The writing changes yet again when the note is seen from behind. (00:13:35)