Deliberate mistake: Right before Rick grabs the half of the broken dagger, he is starting to stand up, only to be kicked by the Dragon Emperor and slid back about 8 feet. As he starts to stand again, you can see that the background is exactly the same as the first time he tried to stand up- meaning that both moments were taken from the same shot, despite the fact that the background should now be different.
Deliberate mistake: When the Dragon Emperor is giving his Terracotta army the speech near the end, you see a shot that pans across the faces of several of his soldiers. A few shots later, this exact same shot is played in reverse. It is very easy to tell if you look at the way the camera moves up and down to catch the different faces.