So I haven't had time to watch Tangled enough to noticed a lot of mistakes, but I found a few. Please forgive me, for there are not very many. But I will do my best to entertain you! Let's begin...
The chain: When Gothel chains Flynn to the wall, and we can see the chain is right up his wrist. We also know that it is at it's maximum point of falling down his arm and cannot go any further. Observe:
The chain is a major part of this scene and it's reasoning for it, so it's kinda hard to miss it.