Other mistake: The two headed monster's heads are pretty big. Big enough to swallow a person whole. But when Val Kilmer jumps on one to impale it, the sword comes out of the bottom of the monster's head. For this to happen, the sword would have to be unbelievably large, larger than a man, which he would be unable to wield anyway.
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.
Continuity mistake: When Raziel shows Bavmorda that she has Cherlindreas' wand, she is wet from all of the rain. In the next scene, when she says that Elora will be queen, she is now completely dry.
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.
Other mistake: Near the end when they reach the castle, the drawbridge isn't even closed properly, they could easily climb up the side of the drawbridge and into the castle. What's the point of having a drawbridge that doesn't close.
Continuity mistake: When Madmartigan closes the front doors and goes to place the wooden crossbar into the brackets, the right side of the crossbar isn't set inside the bracket, it's flush on the outside, and below the gap. When the shot changes, it's now in the bracket without him lifting it up or anything.
Continuity mistake: On the cart, Madmartigan is face-up with a baddie on top of him. Madmartigan punches him with his right fist so the baddie should fall backwards or to the left. However, shot changes and not only is Madmartigan magically standing up, but the baddie is falling to the right, as if the punch came from a totally different position.