While Sarah tells the Toby the story, she puts on his cap. She pulls the cap back off her forehead, but in the next shot the cap has been pulled forward again.
When Jareth throws Toby in the air and the goblin catches him during the song "Dance Magic," it is clearly obvious that Toby is replaced with a baby doll.
Approximately 1 hour and 32 minutes into the film, the Goblin King conjures a glass sphere. The sphere reflects the image of the Goblin King, but there is a noticeable discrepancy where his lips in the reflection are not synchronized with his actual lip movements while speaking.
When Sarah shatters the glass bubble, she is clearly suspended on wires.
When the ledge that Sarah and Hoggle are standing on above the Bog of Eternal Stench collapses, the mic is visible at the top of the screen.