The Final Sacrifice (1990)

Continuity mistake: When Troy and Rowsdower are standing and looking up at the Lost City that flies up and leaves the planet it is dark. But a few seconds later, while they are still looking upwards towards the city, it is full daylight.

Twotall

Continuity mistake: When Rowsdower is fighting the two cultists that were to execute him in the forest, he falls and gets grass stains all over his white jeans. When he meets Troy in the woods a few minutes later, his jeans are much cleaner, and the next day all of the stains are gone.

Twotall

Plot hole: The day after Troy finds the ancient map in his attic, the thugs come to his house because they know he has it. He never told anyone (he is even shown to actively hide it from his aunt), and there is no way they could know this.

Twotall

Aunt Betty: There. What are you studying?
Troy McGreggor: French Revolution.
Aunt Betty: Oh, that looks more like World War Two.

Zap Rowsdower: What's your name, laddy?
Troy McGreggor: Troy McGreggor.
Zap Rowsdower: I'm Rowsdower... Zap Rowsdower.

Troy McGreggor: Food.