Revealing mistake: When Flynn and Maximus are fighting to get the satchel, it flies off and gets snagged on a tree branch. But you can see it goes through the branch, and not around it.
Suggested correction: If you look closely, it is very clear that it doesn't go through the branch at all, but hangs from the side as it should.
Continuity mistake: As Flynn and Rapunzel are getting out of the river, after they had just escaped the cave, you can see that there is no wound on the palm of his left hand, even though he had just cut it on the rocks before. (00:50:40)
Suggested correction: If you take a longer look and analyse it more closely, you would see that he does still have the cut on his left hand. His left not your left.
Trivia: The one with the eye patch of the Stabbington Brothers, (the ones who wanted to have revenge on Flynn) only says one line in the whole movie: "Play it safe, or go get the crown?"
Suggested correction: No, the other brother said that, the one without the eye patch. The other brother doesn't talk and just makes sounds the whole time.
Continuity mistake: When Flynn is being rescued by the "ruffians", after the second guard is taken, the head guard turns around and Flynn is still handcuffed. Then the head guard is knocked out, and immediately following the other guards break through the rear door and Flynn takes off running. His handcuffs are mysteriously gone. No one removes them.
Suggested correction: The Viking with the horned helmet does. Immediately after the guards break the door, three men are around Flynn (one of them hanging from the ceiling.) One of them is doing something with Flynn's hands.