Continuity mistake: After mowing down all the Immortals during the Sanctuary scene, one Watcher tells another to take their heads because they might be Immortals. You see the Watcher to the left side of the screen and a robed figure to his left about four feet away drawing his sword. Suddenly, that same robed figure is now to the Watcher right side and about two feet away.
Continuity mistake: While Duncan is riding in the taxi, the numbers on the side change from shot to shot.
Other mistake: In the scene where Duncan has been captured by the Watchers and restrained in the upright table, take note of the needle. The camera pans around the Watcher's head and then shows the syringe delivering its contents. Once the dose is fully administered, it can clearly be seen that there is no needle on the end when he holds it down near the Highlander's chest.
Continuity mistake: During the flashback to 1712, Connor and Duncan fight it out with highwaymen who are collecting fake tolls from travelers. Throughout this scene, Duncan McLeod's five-o-clock shadow starts out dark, becoming lighter, then darker, and then almost clean-shaven from shot-to-shot as the fight progresses. This continuity problem persists, to a lesser extent, throughout the film.Charles Austin Miller