Continuity mistake: The package Nigel holds in his arms near the beginning of the episode completely changes between shots.
Revealing mistake: The stunt double's wig in the sword fight at the end is messy and disheveled, yet when it cuts to a close up of Sydney, her hair is silky and flat.
The Legend of the Lost - S2-E4
Other mistake: When the bad guy at the start of the episode runs to chase Sydney and Nigel, his foot kicks the side of the large stone lid which cause it to lift up. If this large piece of stone was real stone it would not have moved at all from being nudged by a foot.