Revealing mistake: When Bavmorda and Raziel struggle for control over Sherlindrea's wand (up in the tower Ceremonial Room), lightning bolt shoot out of the wand's tip, and a monolith (among other things) is blasted. The monolith looks like it has been pieced together from cast plastic parts; the fragments' edges are too smooth.
Revealing mistake: When Cherlindrea starts levitating Elora into Willow's arms (the distanced shot, not the one where Willow takes her), you can, if faintly, see the two wires by which the bundle was pulled up.
Revealing mistake: During a battle at the castle where a troll turns into a huge 2-headed monster, Willow charges with a sword. However, the sword wobbles; it's a rubber sword.