Lighting during outdoor scenes changes drastically from shot to shot.
When the boys were in the old mansion, there were a lot of film cuts throughout the film.
When various characters move around carrying candles or lit matches in otherwise dark rooms, the upraised arms, candles and matches are lit, casting shadows of them on the walls behind.
Several of the "nighttime" shots were clearly shot during the day, as evidenced by severe shadows.
When going through the cemetery, Glimpy puts his hand on a gravestone and it wiggles.
When Scruno begs the spider to come back, wires can be seen pulling both the tobacco jar and the miniature skeleton head that pops out of it.