Revealing mistake: When Robin crashes through the stained glass window to save Marian and fight the sheriff, the panes of glass flutter in the breeze, revealing it to be fake glass.
Revealing mistake: When Robin gets attacked by Marian, Robin pushes her towards a stone wall several times, and the wall moves from the impacts.
Revealing mistake: The fallen tree from which Robin gives his inspirational speech about freedom has obviously had several branches removed with a chainsaw. It may be hard to see the marks of the blade on a copy of the video, but in the cinema they were pretty obvious.
Revealing mistake: When Friar Tuck hits his head on an over-hanging branch whilst on his cart, it is really obvious his head comes into contact much earlier than the added sound effect and his eventual reaction would suggest. Plus the branch bends and flexes backwards an awful lot - it's not resistant enough to knock someone out as depicted.