Continuity mistake: When Dumbledore, Fudge, and Moody are talking about Crouch, at one point it says, "said Crouch angrily." Crouch wasn't in the room - they were only talking about him.
Continuity mistake: In chapter 35, the book says '"The Imperius Curse," Moody said.' However, the Polyjuice Potion has already worn off, so it should be Barty Crouch Jr. speaking.
Continuity mistake: When Harry is tied up against Tom Riddle's tombstone, it says that his wand is at his feet. Later, Voldemort tells Wormtail to fetch Harry's wand so that they may duel. Wormtail then retrieves Harry's wand from over near Cedric's body.