Plot hole: The Chinese army displays a great variety of (often anachronistic) weapons and they spent considerable resources arming and reinforcing the Great Wall to challenge the beasts who have been plaguing their land every 60 years for thousands of years. but despite having records of magnets being effective against them, with magnets being well known to them for centuries (early magnetic compasses were available in the IV century BC, and the movie is set in the XI century) they made no use of that at all.
Continuity mistake: When they are in the big hall he goes to demonstrate that he can shoot. He shoots 5 arrows. When you see the arrows hit the bowl only three hit. (00:32:00)
Sometimes he shoots 2 at a time. He does shoot 3 times, but he shoots five arrows.
The correction is valid. He never shoots 2 arrows at once. You may need to watch in slow motion if you can't see what happened. He grabs 3 arrows with his right hand and keeps them in his hand as he shoots 1 arrow at a time. This is probably most obvious on the 2nd shot where you see the 2 arrows in the bow, but when he releases his hand, you see one arrow still in his right hand and 1 arrow leaving the bow.
He starts holding all 3 arrows, shoots 1, reloads holding 2, shoots 1, then reloads and shoots the last arrow.
Continuity mistake: When Strategist Wang uses the magnet tied to a pole to sedate the caged Tao Tei, the pole ends with a hook that does not appear in the POV shots. (00:59:00)
