Continuity mistake: When Lucy awakens at 4:00 AM she checks on Linus and then puts him to bed. In some shots there's a window over Linus' bed, but in other shots the window has vanished, and there's only a shelf over the bed. (00:23:10)
Visible crew/equipment: As the Batcoper emerges from its hangar, multiple crew and equipment are reflected in the cockpit's glass bubble. (00:04:05)
Revealing mistake: When the stagecoach driver gets hit with an arrow, it springs up from below into a horizontal position. (00:33:55)
Other mistake: After the Grinch sends Cindy Lou Who to bed and closes the door, part of his Santa suit becomes the same colour as the background mid-shot.